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2.5: Chapter 6 - Probable Cause and Reasonable Suspicion

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    The Fourth Amendment provides that “no warrants shall issue, but upon probable cause.” Accordingly, warrants (and the searches that followed in the wake of their issuance) have been challenged on the ground that police did not provide sufficient evidence when obtaining the warrants from judges. In addition, the Court has held that in several common situations, police may conduct searches and seizures without a warrant, but only with probable cause. For example, the vehicle searches described in Florida v. Harris (Chapter 5) were permissible under the “automobile exception” to the warrant requirement, about which we will learn more later. In Illinois v. Gates, the Court set forth a new standard for when an informant’s tip provides probable cause to justify a search or arrest.

    Supreme Court of the United States

    Illinois v. Lance Gates

    Decided June 8, 1983 – 462 U.S. 213

    Justice REHNQUIST delivered the opinion of the Court.

    Respondents Lance and Susan Gates were indicted for violation of state drug laws after police officers, executing a search warrant, discovered marijuana and other contraband in their automobile and home. Prior to trial the Gateses moved to suppress evidence seized during this search. The Illinois Supreme Court affirmed the decisions of lower state courts, granting the motion. It held that the affidavit submitted in support of the State’s application for a warrant to search the Gateses’ property was inadequate under this Court’s decisions in Aguilar v. Texas, 378 U.S. 108 (1964) and Spinelli v. United States, 393 U.S. 410 (1969).

    We granted certiorari to consider the application of the Fourth Amendment to a magistrate’s issuance of a search warrant on the basis of a partially corroborated anonymous informant’s tip.

    We conclude that the Illinois Supreme Court read the requirements of our Fourth Amendment decisions too restrictively.


    We now decide whether respondents’ rights under the Fourth and Fourteenth Amendments were violated by the search of their car and house. A chronological statement of events usefully introduces the issues at stake. Bloomingdale, Ill., is a suburb of Chicago located in DuPage County. On May 3, 1978, the Bloomingdale Police Department received by mail an anonymous handwritten letter which read as follows:

    “This letter is to inform you that you have a couple in your town who strictly make their living on selling drugs. They are Sue and Lance Gates, they live on Greenway, off Bloomingdale Rd. in the condominiums. Most of their buys are done in Florida. Sue his wife drives their car to Florida, where she leaves it to be loaded up with drugs, then Lance flys down and drives it back. Sue flys back after she drops the car off in Florida. May 3 she is driving down there again and Lance will be flying down in a few days to drive it back. At the time Lance drives the car back he has the trunk loaded with over $100,000.00 in drugs. Presently they have over $100,000.00 worth of drugs in their basement.

    “They brag about the fact they never have to work, and make their entire living on pushers.”

    “I guarantee if you watch them carefully you will make a big catch. They are friends with some big drugs dealers, who visit their house often.”

    The letter was referred by the Chief of Police of the Bloomingdale Police Department to Detective Mader, who decided to pursue the tip. Mader learned, from the office of the Illinois Secretary of State, that an Illinois driver’s license had been issued to one Lance Gates, residing at a stated address in Bloomingdale. He contacted a confidential informant, whose examination of certain financial records revealed a more recent address for the Gates, and he also learned from a police officer assigned to O’Hare Airport that “L. Gates” had made a reservation on Eastern Airlines flight 245 to West Palm Beach, Fla., scheduled to depart from Chicago on May 5 at 4:15 p.m.

    Mader then made arrangements with an agent of the Drug Enforcement Administration for surveillance of the May 5 Eastern Airlines flight. The agent later reported to Mader that Gates had boarded the flight, and that federal agents in Florida had observed him arrive in West Palm Beach and take a taxi to the nearby Holiday Inn. They also reported that Gates went to a room registered to one Susan Gates and that, at 7:00 a.m. the next morning, Gates and an unidentified woman left the motel in a Mercury bearing Illinois license plates and drove northbound on an interstate frequently used by travelers to the Chicago area. In addition, the DEA agent informed Mader that the license plate number on the Mercury registered to a Hornet station wagon owned by Gates. The agent also advised Mader that the driving time between West Palm Beach and Bloomingdale was approximately 22 to 24 hours.

    Mader signed an affidavit setting forth the foregoing facts, and submitted it to a judge of the Circuit Court of DuPage County, together with a copy of the anonymous letter. The judge of that court thereupon issued a search warrant for the Gateses’ residence and for their automobile. The judge, in deciding to issue the warrant, could have determined that the modus operandi of the Gates had been substantially corroborated. As the anonymous letter predicted, Lance Gates had flown from Chicago to West Palm Beach late in the afternoon of May 5th, had checked into a hotel room registered in the name of his wife, and, at 7:00 a.m. the following morning, had headed north, accompanied by an unidentified woman, out of West Palm Beach on an interstate highway used by travelers from South Florida to Chicago in an automobile bearing a license plate issued to him.

    At 5:15 a.m. on March 7th, only 36 hours after he had flown out of Chicago, Lance Gates, and his wife, returned to their home in Bloomingdale, driving the car in which they had left West Palm Beach some 22 hours earlier. The Bloomingdale police were awaiting them, searched the trunk of the Mercury, and uncovered approximately 350 pounds of marijuana. A search of the Gateses’ home revealed marijuana, weapons, and other contraband. The Illinois Circuit Court ordered suppression of all these items, on the ground that the affidavit submitted to the Circuit Judge failed to support the necessary determination of probable cause to believe that the Gateses’ automobile and home contained the contraband in question. This decision was affirmed in turn by the Illinois Appellate Court and by a divided vote of the Supreme Court of Illinois.

    The Illinois Supreme Court concluded—and we are inclined to agree—that, standing alone, the anonymous letter sent to the Bloomingdale Police Department would not provide the basis for a magistrate’s determination that there was probable cause to believe contraband would be found in the Gateses’ car and home. The letter provides virtually nothing from which one might conclude that its author is either honest or his information reliable; likewise, the letter gives absolutely no indication of the basis for the writer’s predictions regarding the Gateses’ criminal activities. Something more was required, then, before a magistrate could conclude that there was probable cause to believe that contraband would be found in the Gateses’ home and car.

    The Illinois Supreme Court also properly recognized that Detective Mader’s affidavit might be capable of supplementing the anonymous letter with information sufficient to permit a determination of probable cause. In holding that the affidavit in fact did not contain sufficient additional information to sustain a determination of probable cause, the Illinois court applied a “two-pronged test,” derived from our decision in Spinelli v. United States, 393 U.S. 410 (1969). The Illinois Supreme Court, like some others, apparently understood Spinelli as requiring that the anonymous letter satisfy each of two independent requirements before it could be relied on. According to this view, the letter, as supplemented by Mader’s affidavit, first had to adequately reveal the “basis of knowledge” of the letter writer—the particular means by which he came by the information given in his report. Second, it had to provide facts sufficiently establishing either the “veracity” of the affiant’s informant, or, alternatively, the “reliability” of the informant’s report in this particular case.

    The Illinois court, alluding to an elaborate set of legal rules that have developed among various lower courts to enforce the “two-pronged test,” found that the test had not been satisfied. First, the “veracity” prong was not satisfied because, “there was simply no basis [for] … conclud[ing] that the anonymous person [who wrote the letter to the Bloomingdale Police Department] was credible.” The court indicated that corroboration by police of details contained in the letter might never satisfy the “veracity” prong, and in any event, could not do so if, as in the present case, only “innocent” details are corroborated. In addition, the letter gave no indication of the basis of its writer’s knowledge of the Gateses’ activities. The Illinois court understood Spinelli as permitting the detail contained in a tip to be used to infer that the informant had a reliable basis for his statements, but it thought that the anonymous letter failed to provide sufficient detail to permit such an inference. Thus, it concluded that no showing of probable cause had been made.

    We agree with the Illinois Supreme Court that an informant’s “veracity,” “reliability” and “basis of knowledge” are all highly relevant in determining the value of his report. We do not agree, however, that these elements should be understood as entirely separate and independent requirements to be rigidly exacted in every case, which the opinion of the Supreme Court of Illinois would imply. Rather, as detailed below, they should be understood simply as closely intertwined issues that may usefully illuminate the commonsense, practical question whether there is “probable cause” to believe that contraband or evidence is located in a particular place.


    This totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific “tests” be satisfied by every informant’s tip. Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a “practical, nontechnical conception.” “In dealing with probable cause, … as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.” Our observation in United States v. Cortez, 449 U.S. 411, 418 (1981) regarding “particularized suspicion,” is also applicable to the probable cause standard:

    “The process does not deal with hard certainties, but with probabilities. Long before the law of probabilities was articulated as such, practical people formulated certain common-sense conclusions about human behavior; jurors as factfinders are permitted to do the same—and so are law enforcement officers. Finally, the evidence thus collected must be seen and weighed not in terms of library analysis by scholars, but as understood by those versed in the field of law enforcement.”

    As these comments illustrate, probable cause is a fluid concept—turning on the assessment of probabilities in particular factual contexts—not readily, or even usefully, reduced to a neat set of legal rules. Informants’ tips doubtless come in many shapes and sizes from many different types of persons.

    Moreover, the “two-pronged test” directs analysis into two largely independent channels—the informant’s “veracity” or “reliability” and his “basis of knowledge.” There are persuasive arguments against according these two elements such independent status. Instead, they are better understood as relevant considerations in the totality-of-the-circumstances analysis that traditionally has guided probable cause determinations: a deficiency in one may be compensated for, in determining the overall reliability of a tip, by a strong showing as to the other, or by some other indicia of reliability.

    If, for example, a particular informant is known for the unusual reliability of his predictions of certain types of criminal activities in a locality, his failure, in a particular case, to thoroughly set forth the basis of his knowledge surely should not serve as an absolute bar to a finding of probable cause based on his tip. Likewise, if an unquestionably honest citizen comes forward with a report of criminal activity—which if fabricated would subject him to criminal liability—we have found rigorous scrutiny of the basis of his knowledge unnecessary. Conversely, even if we entertain some doubt as to an informant’s motives, his explicit and detailed description of alleged wrongdoing, along with a statement that the event was observed first-hand, entitles his tip to greater weight than might otherwise be the case. Unlike a totality-of-the-circumstances analysis, which permits a balanced assessment of the relative weights of all the various indicia of reliability (and unreliability) attending an informant’s tip, the “two-pronged test” has encouraged an excessively technical dissection of informants’ tips, with undue attention being focused on isolated issues that cannot sensibly be divorced from the other facts presented to the magistrate.

    Finely-tuned standards such as proof beyond a reasonable doubt or by a preponderance of the evidence, useful in formal trials, have no place in the magistrate’s decision. While an effort to fix some general, numerically precise degree of certainty corresponding to “probable cause” may not be helpful, it is clear that “only the probability, and not a prima facie showing, of criminal activity is the standard of probable cause.”

    We also have recognized that affidavits “are normally drafted by nonlawyers in the midst and haste of a criminal investigation. Technical requirements of elaborate specificity once exacted under common law pleading have no proper place in this area.” Likewise, search and arrest warrants long have been issued by persons who are neither lawyers nor judges, and who certainly do not remain abreast of each judicial refinement of the nature of “probable cause.” The rigorous inquiry into the Spinelli prongs and the complex superstructure of evidentiary and analytical rules that some have seen implicit in our Spinelli decision, cannot be reconciled with the fact that many warrants are—quite properly—issued on the basis of nontechnical, common-sense judgments of laymen applying a standard less demanding than those used in more formal legal proceedings.

    Similarly, we have repeatedly said that after-the-fact scrutiny by courts of the sufficiency of an affidavit should not take the form of de novo review. A magistrate’s “determination of probable cause should be paid great deference by reviewing courts.”

    If the affidavits submitted by police officers are subjected to the type of scrutiny some courts have deemed appropriate, police might well resort to warrantless searches, with the hope of relying on consent or some other exception to the warrant clause that might develop at the time of the search. In addition, the possession of a warrant by officers conducting an arrest or search greatly reduces the perception of unlawful or intrusive police conduct, by assuring “the individual whose property is searched or seized of the lawful authority of the executing officer, his need to search, and the limits of his power to search.”

    Finally, the direction taken by decisions following Spinelli poorly serves “the most basic function of any government”: “to provide for the security of the individual and of his property.” The strictures that inevitably accompany the “two-pronged test” cannot avoid seriously impeding the task of law enforcement. If, as the Illinois Supreme Court apparently thought, that test must be rigorously applied in every case, anonymous tips would be of greatly diminished value in police work. Ordinary citizens, like ordinary witnesses, generally do not provide extensive recitations of the basis of their everyday observations. Likewise, as the Illinois Supreme Court observed in this case, the veracity of persons supplying anonymous tips is by hypothesis largely unknown, and unknowable. As a result, anonymous tips seldom could survive a rigorous application of either of the Spinelli prongs. Yet, such tips, particularly when supplemented by independent police investigation, frequently contribute to the solution of otherwise “perfect crimes.” While a conscientious assessment of the basis for crediting such tips is required by the Fourth Amendment, a standard that leaves virtually no place for anonymous citizen informants is not.

    For all these reasons, we conclude that it is wiser to abandon the “two-pronged test” established by our decisions in Aguilar and Spinelli. In its place we reaffirm the totality-of-the-circumstances analysis that traditionally has informed probable cause determinations. The task of the issuing magistrate is simply to make a practical, common-sense decision whether, given all the circumstances set forth in the affidavit before him, including the “veracity” and “basis of knowledge” of persons supplying hearsay information, there is a fair probability that contraband or evidence of a crime will be found in a particular place. And the duty of a reviewing court is simply to ensure that the magistrate had a “substantial basis for … conclud[ing]” that probable cause existed. We are convinced that this flexible, easily applied standard will better achieve the accommodation of public and private interests that the Fourth Amendment requires than does the approach that has developed from Aguilar and Spinelli.

    Our earlier cases illustrate the limits beyond which a magistrate may not venture in issuing a warrant. A sworn statement of an affiant that “he has cause to suspect and does believe that” liquor illegally brought into the United States is located on certain premises will not do. An affidavit must provide the magistrate with a substantial basis for determining the existence of probable cause, and [a] wholly conclusory statement fail[s] to meet this requirement. An officer’s statement that “affiants have received reliable information from a credible person and believe” that heroin is stored in a home, is likewise inadequate. [T]his is a mere conclusory statement that gives the magistrate virtually no basis at all for making a judgment regarding probable cause. Sufficient information must be presented to the magistrate to allow that official to determine probable cause; his action cannot be a mere ratification of the bare conclusions of others. In order to ensure that such an abdication of the magistrate’s duty does not occur, courts must continue to conscientiously review the sufficiency of affidavits on which warrants are issued. But when we move beyond the “bare bones” affidavits this area simply does not lend itself to a prescribed set of rules, like that which had developed from Spinelli. Instead, the flexible, common-sense standard better serves the purposes of the Fourth Amendment’s probable cause requirement.


    Our decisions applying the totality-of-the-circumstances analysis outlined above have consistently recognized the value of corroboration of details of an informant’s tip by independent police work. Likewise, we recognized the probative value of corroborative efforts of police officials in Aguilar—the source of the “two-pronged test”—by observing that if the police had made some effort to corroborate the informant’s report at issue, “an entirely different case” would have been presented.

    The showing of probable cause in the present case was fully compelling. Even standing alone, the facts obtained through the independent investigation of Mader and the DEA at least suggested that the Gateses were involved in drug trafficking. In addition to being a popular vacation site, Florida is well-known as a source of narcotics and other illegal drugs. Lance Gates’ flight to Palm Beach, his brief, overnight stay in a motel, and apparent immediate return north to Chicago in the family car, conveniently awaiting him in West Palm Beach, is as suggestive of a pre-arranged drug run, as it is of an ordinary vacation trip.

    In addition, the judge could rely on the anonymous letter, which had been corroborated in major part by Mader’s efforts. The corroboration of the letter’s predictions that the Gateses’ car would be in Florida, that Lance Gates would fly to Florida in the next day or so, and that he would drive the car north toward Bloomingdale all indicated, albeit not with certainty, that the informant’s other assertions also were true. “Because an informant is right about some things, he is more probably right about other facts” including the claim regarding the Gateses’ illegal activity. This may well not be the type of “reliability” or “veracity” necessary to satisfy some views of the “veracity prong” of Spinelli, but we think it suffices for the practical, common-sense judgment called for in making a probable cause determination. It is enough, for purposes of assessing probable cause, that “corroboration through other sources of information reduced the chances of a reckless or prevaricating tale,” thus providing “a substantial basis for crediting the hearsay.”

    Finally, the anonymous letter contained a range of details relating not just to easily obtained facts and conditions existing at the time of the tip, but to future actions of third parties ordinarily not easily predicted. The letter writer’s accurate information as to the travel plans of each of the Gateses was of a character likely obtained only from the Gateses themselves, or from someone familiar with their not entirely ordinary travel plans. If the informant had access to accurate information of this type a magistrate could properly conclude that it was not unlikely that he also had access to reliable information of the Gateses’ alleged illegal activities. Of course, the Gateses’ travel plans might have been learned from a talkative neighbor or travel agent; under the “two-pronged test” developed from Spinelli, the character of the details in the anonymous letter might well not permit a sufficiently clear inference regarding the letter writer’s “basis of knowledge.” But, as discussed previously, probable cause does not demand the certainty we associate with formal trials. It is enough that there was a fair probability that the writer of the anonymous letter had obtained his entire story either from the Gateses or someone they trusted. And corroboration of major portions of the letter’s predictions provides just this probability. It is apparent, therefore, that the judge issuing the warrant had a “substantial basis for … conclud[ing]” that probable cause to search the Gateses’ home and car existed. The judgment of the Supreme Court of Illinois therefore must be


    Justice BRENNAN, with whom Justice MARSHALL joins, dissenting.

    I write to dissent from the Court’s unjustified and ill-advised rejection of the two-prong test for evaluating the validity of a warrant based on hearsay announced in Aguilar v. Texas, 378 U.S. 108 (1964), and refined in Spinelli v. United States, 393 U.S. 410 (1969).


    In recognition of the judiciary’s role as the only effective guardian of Fourth Amendment rights, this Court has developed over the last half century a set of coherent rules governing a magistrate’s consideration of a warrant application and the showings that are necessary to support a finding of probable cause. We start with the proposition that a neutral and detached magistrate, and not the police, should determine whether there is probable cause to support the issuance of a warrant.

    In order to emphasize the magistrate’s role as an independent arbiter of probable cause and to insure that searches or seizures are not effected on less than probable cause, the Court has insisted that police officers provide magistrates with the underlying facts and circumstances that support the officers’ conclusions. The Court stated that “[u]nder the Fourth Amendment, an officer may not properly issue a warrant to search a private dwelling unless he can find probable cause therefor from facts or circumstances presented to him under oath or affirmation. Mere affirmance of belief or suspicion is not enough.”

    [Our previous cases] advance an important [ ] substantive value: Findings of probable cause, and attendant intrusions, should not be authorized unless there is some assurance that the information on which they are based has been obtained in a reliable way by an honest or credible person. As applied to police officers, the rules focus on the way in which the information was acquired. As applied to informants, the rules focus both on the honesty or credibility of the informant and on the reliability of the way in which the information was acquired. Insofar as it is more complicated, an evaluation of affidavits based on hearsay involves a more difficult inquiry. This suggests a need to structure the inquiry in an effort to insure greater accuracy. The standards announced in Aguilar, as refined by Spinelli, fulfill that need. The standards inform the police of what information they have to provide and magistrates of what information they should demand. The standards also inform magistrates of the subsidiary findings they must make in order to arrive at an ultimate finding of probable cause. By requiring police to provide certain crucial information to magistrates and by structuring magistrates’ probable cause inquiries, Aguilar and Spinelli assure the magistrate’s role as an independent arbiter of probable cause, insure greater accuracy in probable cause determinations, and advance the substantive value identified above.

    Until today the Court has never squarely addressed the application of the Aguilar and Spinelli standards to tips from anonymous informants. By definition nothing is known about an anonymous informant’s identity, honesty, or reliability. One commentator has suggested that anonymous informants should be treated as presumptively unreliable. In any event, there certainly is no basis for treating anonymous informants as presumptively reliable. Nor is there any basis for assuming that the information provided by an anonymous informant has been obtained in a reliable way. If we are unwilling to accept conclusory allegations from the police, who are presumptively reliable, or from informants who are known, at least to the police, there cannot possibly be any rational basis for accepting conclusory allegations from anonymous informants.


    In rejecting the Aguilar-Spinelli standards, the Court suggests that a “totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific ‘tests’ be satisfied by every informant’s tip.” In support of this proposition the Court relies on the “practical, nontechnical” nature of probable cause.

    [O]ne can concede that probable cause is a “practical, nontechnical” concept without betraying the values that Aguilar and Spinelli reflect. As noted, Aguilar and Spinelli require the police to provide magistrates with certain crucial information. They also provide structure for magistrates’ probable cause inquiries. In so doing, Aguilar and Spinelli preserve the role of magistrates as independent arbiters of probable cause, insure greater accuracy in probable cause determinations, and advance the substantive value of precluding findings of probable cause, and attendant intrusions, based on anything less than information from an honest or credible person who has acquired his information in a reliable way. Neither the standards nor their effects are inconsistent with a “practical, nontechnical” conception of probable cause. Once a magistrate has determined that he has information before him that he can reasonably say has been obtained in a reliable way by a credible person, he has ample room to use his common sense and to apply a practical, nontechnical conception of probable cause.

    At the heart of the Court’s decision to abandon Aguilar and Spinelli appears to be its belief that “the direction taken by decisions following Spinelli poorly serves ‘the most basic function of any government: to provide for the security of the individual and of his property.’” This conclusion rests on the judgment that Aguilar and Spinelli “seriously imped[e] the task of law enforcement,” and render anonymous tips valueless in police work. Surely, the Court overstates its case. But of particular concern to all Americans must be that the Court gives virtually no consideration to the value of insuring that findings of probable cause are based on information that a magistrate can reasonably say has been obtained in a reliable way by an honest or credible person.


    The Court’s complete failure to provide any persuasive reason for rejecting Aguilar and Spinelli doubtlessly reflects impatience with what it perceives to be “overly technical” rules governing searches and seizures under the Fourth Amendment. Words such as “practical,” “nontechnical,” and “commonsense,” as used in the Court’s opinion, are but code words for an overly permissive attitude towards police practices in derogation of the rights secured by the Fourth Amendment. Everyone shares the Court’s concern over the horrors of drug trafficking, but under our Constitution only measures consistent with the Fourth Amendment may be employed by government to cure this evil. We must be ever mindful of Justice Stewart’s admonition in Coolidge v. New Hampshire, 403 U.S. 443 (1971), that “[i]n times of unrest, whether caused by crime or racial conflict or fear of internal subversion, this basic law and the values that it represents may appear unrealistic or ‘extravagant’ to some. But the values were those of the authors of our fundamental constitutional concepts.” In the same vein, Glasser v. United States, 315 U.S. 60 (1942), warned that “[s]teps innocently taken may, one by one, lead to the irretrievable impairment of substantial liberties.”

    Rights secured by the Fourth Amendment are particularly difficult to protect because their “advocates are usually criminals.” But the rules “we fashion [are] for the innocent and guilty alike.” By replacing Aguilar and Spinelli with a test that provides no assurance that magistrates, rather than the police, or informants, will make determinations of probable cause; imposes no structure on magistrates’ probable cause inquiries; and invites the possibility that intrusions may be justified on less than reliable information from an honest or credible person, today’s decision threatens to “obliterate one of the most fundamental distinctions between our form of government, where officers are under the law, and the police-state where they are the law.”

    Notes, Comments, and Questions

    The Gates Court rejects the Aguilar-Spinelli test’s insistence on using two specific measures to compose a (somewhat) mathematical formula for probable cause. As the Court explains, the existence of probable cause will not be found by entering “veracity” and “basis of knowledge” into a formula which yields the total weight of evidence presented to a magistrate. (The graph below exemplifies how such a formula might work.)

    Image No. 4

    As the Court puts it:

    “This totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific ‘tests’ be satisfied by every informant’s tip. Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a ‘practical, nontechnical conception.’”

    When police have probable cause to believe either (1) that evidence of crime will be found in a particular place or (2) that a certain person has committed a crime, important police action becomes lawful that would have remained unlawful absent probable cause. One important example involves vehicle stops; police may stop a car based on probable cause to believe that its driver has committed a traffic law violation. It is widely believed that many officers use this power for reasons other than traffic enforcement—for example, stopping drivers who violate trivial traffic rules in the hope of discovering evidence of more serious lawbreaking. In addition, some critics of police allege that at least some officers use their traffic-stop authority in ways that constitute unlawful discrimination, such as on the basis of race. Based on these beliefs and allegations, motorists have sought review of vehicle stops, justified by probable cause, on the basis of police officers’ “real” or “true” reasons for conducting the stops. The Court has resisted engaging in such review.

    Supreme Court of the United States

    Michael A. Whren v. United States

    Decided June 10, 1996 – 517 U.S. 806

    Justice SCALIA delivered the opinion of the [unanimous] Court.

    In this case we decide whether the temporary detention of a motorist who the police have probable cause to believe has committed a civil traffic violation is inconsistent with the Fourth Amendment’s prohibition against unreasonable seizures unless a reasonable officer would have been motivated to stop the car by a desire to enforce the traffic laws.


    On the evening of June 10, 1993, plainclothes vice-squad officers of the District of Columbia Metropolitan Police Department were patrolling a “high drug area” of the city in an unmarked car. Their suspicions were aroused when they passed a dark Pathfinder truck with temporary license plates and youthful occupants waiting at a stop sign, the driver looking down into the lap of the passenger at his right. The truck remained stopped at the intersection for what seemed an unusually long time—more than 20 seconds. When the police car executed a U-turn in order to head back toward the truck, the Pathfinder turned suddenly to its right, without signaling, and sped off at an “unreasonable” speed. The policemen followed, and in a short while overtook the Pathfinder when it stopped behind other traffic at a red light. They pulled up alongside, and Officer Ephraim Soto stepped out and approached the driver’s door, identifying himself as a police officer and directing the driver, petitioner Brown, to put the vehicle in park. When Soto drew up to the driver’s window, he immediately observed two large plastic bags of what appeared to be crack cocaine in petitioner Whren’s hands. Petitioners were arrested, and quantities of several types of illegal drugs were retrieved from the vehicle.

    Petitioners were charged in a four-count indictment with violating various federal drug laws. At a pretrial suppression hearing, they challenged the legality of the stop and the resulting seizure of the drugs. They argued that the stop had not been justified by probable cause to believe, or even reasonable suspicion, that petitioners were engaged in illegal drug-dealing activity; and that Officer Soto’s asserted ground for approaching the vehicle—to give the driver a warning concerning traffic violations—was pretextual. The District Court denied the suppression motion, concluding that “the facts of the stop were not controverted,” and “[t]here was nothing to really demonstrate that the actions of the officers were contrary to a normal traffic stop.”

    Petitioners were convicted of the counts at issue here. The Court of Appeals affirmed the convictions, holding with respect to the suppression issue that, “regardless of whether a police officer subjectively believes that the occupants of an automobile may be engaging in some other illegal behavior, a traffic stop is permissible as long as a reasonable officer in the same circumstances could have stopped the car for the suspected traffic violation.” We granted certiorari.


    The Fourth Amendment guarantees “[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” Temporary detention of individuals during the stop of an automobile by the police, even if only for a brief period and for a limited purpose, constitutes a “seizure” of “persons” within the meaning of this provision. An automobile stop is thus subject to the constitutional imperative that it not be “unreasonable” under the circumstances. As a general matter, the decision to stop an automobile is reasonable where the police have probable cause to believe that a traffic violation has occurred.

    Petitioners accept that Officer Soto had probable cause to believe that various provisions of the District of Columbia traffic code had been violated. They argue, however, that “in the unique context of civil traffic regulations” probable cause is not enough. Since, they contend, the use of automobiles is so heavily and minutely regulated that total compliance with traffic and safety rules is nearly impossible, a police officer will almost invariably be able to catch any given motorist in a technical violation. This creates the temptation to use traffic stops as a means of investigating other law violations, as to which no probable cause or even articulable suspicion exists. Petitioners, who are both black, further contend that police officers might decide which motorists to stop based on decidedly impermissible factors, such as the race of the car’s occupants. To avoid this danger, they say, the Fourth Amendment test for traffic stops should be, not the normal one (applied by the Court of Appeals) of whether probable cause existed to justify the stop; but rather, whether a police officer, acting reasonably, would have made the stop for the reason given.


    Petitioners contend that the standard they propose is consistent with our past cases’ disapproval of police attempts to use valid bases of action against citizens as pretexts for pursuing other investigatory agendas. We are reminded that [in previous cases] we stated that “an inventory search” must not be a ruse for a general rummaging in order to discover incriminating evidence”; that in approving an inventory search, we apparently thought it significant that there had been “no showing that the police, who were following standardized procedures, acted in bad faith or for the sole purpose of investigation”; and that we observed, in upholding the constitutionality of a warrantless administrative inspection, that the search did not appear to be “a ‘pretext’ for obtaining evidence of … violation of … penal laws.” But only an undiscerning reader would regard these cases as endorsing the principle that ulterior motives can invalidate police conduct that is justifiable on the basis of probable cause to believe that a violation of law has occurred. In each case we were addressing the validity of a search conducted in the absence of probable cause. Our statements simply explain that the exemption from the need for probable cause (and warrant), which is accorded to searches made for the purpose of inventory or administrative regulation, is not accorded to searches that are not made for those purposes.

    We think [our prior decisions] foreclose any argument that the constitutional reasonableness of traffic stops depends on the actual motivations of the individual officers involved. We of course agree with petitioners that the Constitution prohibits selective enforcement of the law based on considerations such as race. But the constitutional basis for objecting to intentionally discriminatory application of laws is the Equal Protection Clause, not the Fourth Amendment. Subjective intentions play no role in ordinary, probable-cause Fourth Amendment analysis.


    Recognizing that we have been unwilling to entertain Fourth Amendment challenges based on the actual motivations of individual officers, petitioners disavow any intention to make the individual officer’s subjective good faith the touchstone of “reasonableness.” They insist that the standard they have put forward—whether the officer’s conduct deviated materially from usual police practices, so that a reasonable officer in the same circumstances would not have made the stop for the reasons given—is an “objective” one.

    But although framed in empirical terms, this approach is plainly and indisputably driven by subjective considerations. Its whole purpose is to prevent the police from doing under the guise of enforcing the traffic code what they would like to do for different reasons. Petitioners’ proposed standard may not use the word “pretext,” but it is designed to combat nothing other than the perceived “danger” of the pretextual stop, albeit only indirectly and over the run of cases. Instead of asking whether the individual officer had the proper state of mind, the petitioners would have us ask, in effect, whether (based on general police practices) it is plausible to believe that the officer had the proper state of mind.

    Why one would frame a test designed to combat pretext in such fashion that the court cannot take into account actual and admitted pretext is a curiosity that can only be explained by the fact that our cases have foreclosed the more sensible option. If those cases were based only upon the evidentiary difficulty of establishing subjective intent, petitioners’ attempt to root out subjective vices through objective means might make sense. But they were not based only upon that, or indeed even principally upon that. Their principal basis—which applies equally to attempts to reach subjective intent through ostensibly objective means—is simply that the Fourth Amendment’s concern with “reasonableness” allows certain actions to be taken in certain circumstances, whatever the subjective intent. But even if our concern had been only an evidentiary one, petitioners’ proposal would by no means assuage it. Indeed, it seems to us somewhat easier to figure out the intent of an individual officer than to plumb the collective consciousness of law enforcement in order to determine whether a “reasonable officer” would have been moved to act upon the traffic violation. While police manuals and standard procedures may sometimes provide objective assistance, ordinarily one would be reduced to speculating about the hypothetical reaction of a hypothetical constable—an exercise that might be called virtual subjectivity.

    Moreover, police enforcement practices, even if they could be practicably assessed by a judge, vary from place to place and from time to time. We cannot accept that the search and seizure protections of the Fourth Amendment are so variable and can be made to turn upon such trivialities. The difficulty is illustrated by petitioners’ arguments in this case. Their claim that a reasonable officer would not have made this stop is based largely on District of Columbia police regulations which permit plainclothes officers in unmarked vehicles to enforce traffic laws “only in the case of a violation that is so grave as to pose an immediate threat to the safety of others.” This basis of invalidation would not apply in jurisdictions that had a different practice. And it would not have applied even in the District of Columbia, if Officer Soto had been wearing a uniform or patrolling in a marked police cruiser.


    In what would appear to be an elaboration on the “reasonable officer” test, petitioners argue that the balancing inherent in any Fourth Amendment inquiry requires us to weigh the governmental and individual interests implicated in a traffic stop such as we have here. That balancing, petitioners claim, does not support investigation of minor traffic infractions by plainclothes police in unmarked vehicles; such investigation only minimally advances the government’s interest in traffic safety, and may indeed retard it by producing motorist confusion and alarm—a view said to be supported by the Metropolitan Police Department’s own regulations generally prohibiting this practice. And as for the Fourth Amendment interests of the individuals concerned, petitioners point out that our cases acknowledge that even ordinary traffic stops entail “a possibly unsettling show of authority”; that they at best “interfere with freedom of movement, are inconvenient, and consume time” and at worst “may create substantial anxiety.” That anxiety is likely to be even more pronounced when the stop is conducted by plainclothes officers in unmarked cars.

    It is of course true that in principle every Fourth Amendment case, since it turns upon a “reasonableness” determination, involves a balancing of all relevant factors. With rare exceptions not applicable here, however, the result of that balancing is not in doubt where the search or seizure is based upon probable cause.

    Where probable cause has existed, the only cases in which we have found it necessary actually to perform the “balancing” analysis involved searches or seizures conducted in an extraordinary manner, unusually harmful to an individual’s privacy or even physical interests—such as, for example, seizure by means of deadly force, unannounced entry into a home, entry into a home without a warrant, or physical penetration of the body. The making of a traffic stop out of uniform does not remotely qualify as such an extreme practice, and so is governed by the usual rule that probable cause to believe the law has been broken “outbalances” private interest in avoiding police contact.

    Petitioners urge as an extraordinary factor in this case that the “multitude of applicable traffic and equipment regulations” is so large and so difficult to obey perfectly that virtually everyone is guilty of violation, permitting the police to single out almost whomever they wish for a stop. But we are aware of no principle that would allow us to decide at what point a code of law becomes so expansive and so commonly violated that infraction itself can no longer be the ordinary measure of the lawfulness of enforcement. And even if we could identify such exorbitant codes, we do not know by what standard (or what right) we would decide, as petitioners would have us do, which particular provisions are sufficiently important to merit enforcement.

    For the run-of-the-mine case, which this surely is, we think there is no realistic alternative to the traditional common-law rule that probable cause justifies a search and seizure.

    Here the District Court found that the officers had probable cause to believe that petitioners had violated the traffic code. That rendered the stop reasonable under the Fourth Amendment, the evidence thereby discovered admissible, and the upholding of the convictions by the Court of Appeals for the District of Columbia Circuit correct. The judgment is


    Notes, Comments, and Questions

    The unanimous decision by the Court illustrates how important it is to the Justices to avoid creating legal rules and tests that require judges to guess what officers were thinking when performing certain actions. If the admissibility of evidence depends upon the mental state of a police officer during a stressful moment months or even years before a resulting evidentiary hearing, multiple problems are created. First, as a practical matter, determining what the officer was thinking when (for example) stopping a car will not be easy. Second, the officer may be tempted to commit perjury if her mental state was not the “correct” one under the relevant test.

    In addition, the result in Whren exemplifies the Court’s apparent desire to avoid becoming in charge of day-to-day management of police departments. If the Court finds a constitutional requirement for departments to adopt certain best practices, then the Justices must (1) learn enough about policing to decide what practices should be required and (2) eventually hear more cases on whether departments are sufficiently obedient to the Court’s command. These prospects seem unappealing to the Justices. (Similar feelings may inform the Court’s decisions in education law cases. The Court has retreated from supervising school districts despite evidence that school segregation remains a serious problem.)

    The Whren majority noted that if police indeed performed traffic stops on the basis of impermissible reasons related to the race of motorists, the stops might violate the Equal Protection Clause of the Fourteenth Amendment. The savvy reader might ask whether the Fourteenth Amendment applies at all. The traffic stop was in Washington, D.C. If the District of Columbia is not a “state,” and accordingly is not covered by the Fourteenth Amendment, then is racial discrimination allowed (or, to be more precise, is there no constitutional remedy)? The Court decided that there is a remedy. See Bolling v. Sharpe, 347 U.S. 497, 500 (1954), supplemented sub nom. Brown v. Bd. of Educ. of Topeka, Kan., 349 U.S. 294 (1955) (establishing “reverse incorporation” of equal protection against the federal government) (“In view of our decision that the Constitution prohibits the states from maintaining racially segregated public schools, it would be unthinkable that the same Constitution would impose a lesser duty on the Federal Government.”).

    Unfortunately for Whren, the Court has not allowed evidence to be excluded from criminal trials on the basis of Equal Protection violations; the legal remedy for such violations would come from civil lawsuits.

    The Court’s holding in Whren illustrates the power of probable cause. Because the Court is so resistant to examining the motives of officers who take investigatory steps on the basis of probable cause, the term’s definition is of exceptional importance. In a 2018 case, the Court applied the standard set forth in Illinois v. Gates to new facts.

    Supreme Court of the United States

    District of Columbia v. Theodore Wesby

    Decided Jan. 22, 2018 – 138 S. Ct. 577

    Justice THOMAS delivered the opinion of the Court.

    This case involves a civil suit against the District of Columbia and five of its police officers, brought by 16 individuals who were arrested for holding a raucous, late-night party in a house they did not have permission to enter. The United States Court of Appeals for the District of Columbia Circuit held that there was no probable cause to arrest the partygoers, and that the officers were not entitled to qualified immunity. We reverse on both grounds.


    Around 1 a.m. on March 16, 2008, the District’s Metropolitan Police Department received a complaint about loud music and illegal activities at a house in Northeast D.C. The caller, a former neighborhood commissioner, told police that the house had been vacant for several months. When officers arrived at the scene, several neighbors confirmed that the house should have been empty. The officers approached the house and, consistent with the complaint, heard loud music playing inside.

    After the officers knocked on the front door, they saw a man look out the window and then run upstairs. One of the partygoers opened the door, and the officers entered. They immediately observed that the inside of the house “‘was in disarray’” and looked like “‘a vacant property.’” The officers smelled marijuana and saw beer bottles and cups of liquor on the floor. In fact, the floor was so dirty that one of the partygoers refused to sit on it while being questioned. Although the house had working electricity and plumbing, it had no furniture downstairs other than a few padded metal chairs. The only other signs of habitation were blinds on the windows, food in the refrigerator, and toiletries in the bathroom.

    In the living room, the officers found a makeshift strip club. Several women were wearing only bras and thongs, with cash tucked into their garter belts. The women were giving lap dances while other partygoers watched. Most of the onlookers were holding cash and cups of alcohol. After seeing the uniformed officers, many partygoers scattered into other parts of the house.

    The officers found more debauchery upstairs. A naked woman and several men were in the bedroom. A bare mattress—the only one in the house—was on the floor, along with some lit candles and multiple open condom wrappers. A used condom was on the windowsill. The officers found one partygoer hiding in an upstairs closet, and another who had shut himself in the bathroom and refused to come out.

    The officers found a total of 21 people in the house. After interviewing all 21, the officers did not get a clear or consistent story. Many partygoers said they were there for a bachelor party, but no one could identify the bachelor. Each of the partygoers claimed that someone had invited them to the house, but no one could say who. Two of the women working the party said that a woman named “Peaches” or “Tasty” was renting the house and had given them permission to be there. One of the women explained that the previous owner had recently passed away, and Peaches had just started renting the house from the grandson who inherited it. But the house had no boxes or moving supplies. She did not know Peaches’ real name. And Peaches was not there.

    An officer asked the woman to call Peaches on her phone so he could talk to her. Peaches answered and explained that she had just left the party to go to the store. When the officer asked her to return, Peaches refused because she was afraid of being arrested. The sergeant supervising the investigation also spoke with Peaches. At first, Peaches claimed to be renting the house from the owner, who was fixing it up for her. She also said that she had given the attendees permission to have the party. When the sergeant again asked her who had given her permission to use the house, Peaches became evasive and hung up. The sergeant called her back, and she began yelling and insisting that she had permission before hanging up a second time. The officers eventually got Peaches on the phone again, and she admitted that she did not have permission to use the house.

    The officers then contacted the owner. He told them that he had been trying to negotiate a lease with Peaches, but they had not reached an agreement. He confirmed that he had not given Peaches (or anyone else) permission to be in the house—let alone permission to use it for a bachelor party. At that point, the officers arrested the 21 partygoers for unlawful entry. The police transported the partygoers to the police station, where the lieutenant decided to charge them with disorderly conduct. The partygoers were released, and the charges were eventually dropped.


    Respondents, 16 of the 21 partygoers, sued the District and five of the arresting officers. They sued the officers for false arrest under the Fourth Amendment. The partygoers’ claims were all “predicated upon the allegation that [they] were arrested without probable cause.”

    On cross-motions for summary judgment, the District Court awarded partial summary judgment to the partygoers. It concluded that the officers lacked probable cause to arrest the partygoers for unlawful entry.1 The officers were told that Peaches had invited the partygoers to the house, the District Court reasoned, and nothing the officers learned in their investigation suggested the partygoers “‘knew or should have known that [they were] entering against the [owner’s] will.’” The District Court also concluded that the officers were not entitled to qualified immunity under § 1983. It noted that, under District case law, “probable cause to arrest for unlawful entry requires evidence that the alleged intruder knew or should have known, upon entry, that such entry was against the will of the owner.” And in its view, the officers had no such evidence.

    With liability resolved, the case proceeded to trial on damages. The jury awarded the partygoers a total of $680,000 in compensatory damages. After the District Court awarded attorney’s fees, the total award was nearly $1 million.

    On appeal, a divided panel of the D.C. Circuit affirmed. [T]he panel majority made Peaches’ invitation “central” to its determination that the officers lacked probable cause to arrest the partygoers for unlawful entry. The panel majority asserted that, “in the absence of any conflicting information, Peaches’ invitation vitiates the necessary element of [the partygoers’] intent to enter against the will of the lawful owner.” And the panel majority determined that “there is simply no evidence in the record that [the partygoers] had any reason to think the invitation was invalid.”

    We granted certiorari to resolve [] whether the officers had probable cause to arrest the partygoers.


    To determine whether an officer had probable cause for an arrest, “we examine the events leading up to the arrest, and then decide ‘whether these historical facts, viewed from the standpoint of an objectively reasonable police officer, amount to’ probable cause.” Because probable cause “deals with probabilities and depends on the totality of the circumstances,” it is “a fluid concept” that is “not readily, or even usefully, reduced to a neat set of legal rules.” It “requires only a probability or substantial chance of criminal activity, not an actual showing of such activity.” Probable cause “is not a high bar.”


    There is no dispute that the partygoers entered the house against the will of the owner. Nonetheless, the partygoers contend that the officers lacked probable cause to arrest them because the officers had no reason to believe that they “knew or should have known” their “entry was unwanted.” We disagree. Considering the totality of the circumstances, the officers made an “entirely reasonable inference” that the partygoers were knowingly taking advantage of a vacant house as a venue for their late-night party.

    Consider first the condition of the house. Multiple neighbors, including a former neighborhood official, informed the officers that the house had been vacant for several months. The house had no furniture, except for a few padded metal chairs and a bare mattress. The rest of the house was empty, save for some fixtures and large appliances. The house had a few signs of inhabitance—working electricity and plumbing, blinds on the windows, toiletries in the bathroom, and food in the refrigerator. But those facts are not necessarily inconsistent with the house being unoccupied. The owner could have paid the utilities and kept the blinds while he looked for a new tenant, and the partygoers could have brought the food and toiletries. Although one woman told the officers that Peaches had recently moved in, the officers had reason to doubt that was true. There were no boxes or other moving supplies in the house; nor were there other possessions, such as clothes in the closet, suggesting someone lived there.

    In addition to the condition of the house, consider the partygoers’ conduct. The party was still going strong when the officers arrived after 1 a.m., with music so loud that it could be heard from outside. Upon entering the house, multiple officers smelled marijuana. The partygoers left beer bottles and cups of liquor on the floor, and they left the floor so dirty that one of them refused to sit on it. The living room had been converted into a makeshift strip club. Strippers in bras and thongs, with cash stuffed in their garter belts, were giving lap dances. Upstairs, the officers found a group of men with a single, naked woman on a bare mattress—the only bed in the house—along with multiple open condom wrappers and a used condom.

    Taken together, the condition of the house and the conduct of the partygoers allowed the officers to make several “‘common-sense conclusions about human behavior.’” Most homeowners do not live in near-barren houses. And most homeowners do not invite people over to use their living room as a strip club, to have sex in their bedroom, to smoke marijuana inside, and to leave their floors filthy. The officers could thus infer that the partygoers knew their party was not authorized.

    The partygoers’ reaction to the officers gave them further reason to believe that the partygoers knew they lacked permission to be in the house. Many scattered at the sight of the uniformed officers. Two hid themselves, one in a closet and the other in a bathroom. “[U]nprovoked flight upon noticing the police,” we have explained, “is certainly suggestive” of wrongdoing and can be treated as “suspicious behavior” that factors into the totality of the circumstances. In fact, “deliberately furtive actions and flight at the approach of … law officers are strong indicia of mens rea.” A reasonable officer could infer that the partygoers’ scattering and hiding was an indication that they knew they were not supposed to be there.

    The partygoers’ answers to the officers’ questions also suggested their guilty state of mind. When the officers asked who had given them permission to be there, the partygoers gave vague and implausible responses. They could not say who had invited them. Only two people claimed that Peaches had invited them, and they were working the party instead of attending it. If Peaches was the hostess, it was odd that none of the partygoers mentioned her name. Additionally, some of the partygoers claimed the event was a bachelor party, but no one could identify the bachelor. The officers could have disbelieved them, since people normally do not throw a bachelor party without a bachelor. Based on the vagueness and implausibility of the partygoers’ stories, the officers could have reasonably inferred that they were lying and that their lies suggested a guilty mind.

    The panel majority relied heavily on the fact that Peaches said she had invited the partygoers to the house. But when the officers spoke with Peaches, she was nervous, agitated, and evasive. After initially insisting that she had permission to use the house, she ultimately confessed that this was a lie—a fact that the owner confirmed. Peaches’ lying and evasive behavior gave the officers reason to discredit everything she had told them. For example, the officers could have inferred that Peaches lied to them when she said she had invited the others to the house, which was consistent with the fact that hardly anyone at the party knew her name. Or the officers could have inferred that Peaches told the partygoers (like she eventually told the police) that she was not actually renting the house, which was consistent with how the partygoers were treating it.

    Viewing these circumstances as a whole, a reasonable officer could conclude that there was probable cause to believe the partygoers knew they did not have permission to be in the house.


    In concluding otherwise, the panel majority engaged in an “excessively technical dissection” of the factors supporting probable cause. Indeed, the panel majority failed to follow two basic and well-established principles of law.

    First, the panel majority viewed each fact “in isolation, rather than as a factor in the totality of the circumstances.” This was “mistaken in light of our precedents.” The “totality of the circumstances” requires courts to consider “the whole picture.” Our precedents recognize that the whole is often greater than the sum of its parts—especially when the parts are viewed in isolation. Instead of considering the facts as a whole, the panel majority took them one by one. For example, it dismissed the fact that the partygoers “scattered or hid when the police entered the house” because that fact was “not sufficient standing alone to create probable cause.” Similarly, it found “nothing in the record suggesting that the condition of the house, on its own, should have alerted the [partygoers] that they were unwelcome.” The totality-of-the-circumstances test “precludes this sort of divide-and-conquer analysis.”

    Second, the panel majority mistakenly believed that it could dismiss outright any circumstances that were “susceptible of innocent explanation.” For example, the panel majority brushed aside the drinking and the lap dances as “consistent with” the partygoers’ explanation that they were having a bachelor party. And it similarly dismissed the condition of the house as “entirely consistent with” Peaches being a “new tenant.” But probable cause does not require officers to rule out [sic] a suspect’s innocent explanation for suspicious facts. As we have explained, “the relevant inquiry is not whether particular conduct is ‘innocent’ or ‘guilty,’ but the degree of suspicion that attaches to particular types of noncriminal acts.” Thus, the panel majority should have asked whether a reasonable officer could conclude—considering all of the surrounding circumstances, including the plausibility of the explanation itself—that there was a “substantial chance of criminal activity.”

    For all of these reasons, we reverse the D.C. Circuit’s holding that the officers lacked probable cause to arrest. Accordingly, the District and its officers are entitled to summary judgment on all of the partygoers’ claims.

    The judgment of the D.C. Circuit is therefore reversed, and the case is remanded for further proceedings consistent with this opinion.

    Justice GINSBURG, concurring in the judgment in part.

    This case, well described in the opinion of the Court of Appeals, leads me to question whether this Court, in assessing probable cause, should continue to ignore why police in fact acted. No arrests of plaintiffs-respondents were made until Sergeant Suber so instructed. His instruction, when conveyed to the officers he superintended, was based on an error of law. Sergeant Suber believed that the absence of the premises owner’s consent, an uncontested fact in this case, sufficed to justify arrest of the partygoers for unlawful entry. An essential element of unlawful entry in the District of Columbia is that the defendant “knew or should have known that his entry was unwanted.” But under Sergeant Suber’s view of the law, what the arrestees knew or should have known was irrelevant. They could be arrested, as he comprehended the law, even if they believed their entry was invited by a lawful occupant.

    Ultimately, plaintiffs-respondents were not booked for unlawful entry. Instead, they were charged at the police station with disorderly conduct. Yet no police officers at the site testified to having observed any activities warranting a disorderly conduct charge. Quite the opposite. The officers at the scene of the arrest uniformly testified that they had neither seen nor heard anything that would justify such a charge, and Sergeant Suber specifically advised his superiors that the charge was unwarranted.

    The Court’s jurisprudence, I am concerned, sets the balance too heavily in favor of police unaccountability to the detriment of Fourth Amendment protection. A number of commentators have criticized the path we charted in Whren v. United States, 517 U.S. 806 (1996), and follow-on opinions, holding that “an arresting officer’s state of mind … is irrelevant to the existence of probable cause.” I would leave open, for reexamination in a future case, whether a police officer’s reason for acting, in at least some circumstances, should factor into the Fourth Amendment inquiry. Given the current state of the Court’s precedent, however, I agree that the disposition gained by plaintiffs-respondents [i.e., a ruling that officers violated their rights] was not warranted by “settled law.” The defendants-petitioners are therefore sheltered by qualified immunity.

    Notes, Comments, and Questions

    Does the procedural posture of this case change your view on the outcome? This is not a criminal prosecution, in which the defendants are arguing about probable cause to get their charges dismissed. This is a lawsuit by the people at the party, alleging that police violated their clearly established constitutional rights when arresting them.

    The standard for probable cause is not especially high. It’s nothing like proof beyond a reasonable doubt or even preponderance of the evidence. In addition to “probable cause,” the Court has used several cases to define “reasonable suspicion,” which is more than a mere hunch but requires less evidence than probable cause. Certain police conduct—most importantly “stop and frisk”—is permissible on the basis of reasonable suspicion even if officers lack probable cause. We will review reasonable suspicion at length when studying stop and frisk.

    As the semester progresses, students should make a point of noting (1) which police tactics are permissible with no evidence or suspicion whatsoever (for example, investigatory tactics that are not “searches,” such as opening a bag of trash left out for collection), (2) which tactics may not be conducted with no suspicion but are allowed with “reasonable suspicion,” and (3) which police tactics require probable cause. Among those police tactics requiring probable cause, students should note which require warrants.

    The Phenomenon of “Driving While Black” or “Driving While Brown”

    For decades, observers have documented that Black and brown drivers are more likely than white drivers to be stopped by police, a phenomenon sometimes described as “Driving While [Black/Brown]” or “DWB.” (Similar observations have been made about which pedestrians police choose to stop and frisk, a topic to which we will return.) U.S. Senator Tim Scott (R-S.C.) described in a 2016 speech his experiences as a Black motorist, along with incidents in which Capitol police questioned whether he really was a member of the Senate.2 Reporting that he had been stopped by police while driving seven times over the prior year, he asked colleagues to “imagine the frustration, the irritation the sense of a loss of dignity that accompanies each of those stops.”

    Noting that in most of the incidents, “[He] was doing nothing more than driving a new car, in the wrong neighborhood, or some other reason just as trivial,” he said, “I have felt the anger, the frustration, the sadness and the humiliation that comes with feeling that you’re being targeted for nothing more than just being yourself.”

    After being stopped by Capitol police, Sen. Scott received apologies on multiple occasions from police leadership. Most Americans, however, lack the social capital possessed by Senators and cannot expect that sort of response to complaints.

    Although the cause of “DWB” stops is disputed, the existence of the phenomenon is well-documented,3 as are its effects on relations between police departments and minority communities. For example, one of your authors once attended an event in St. Louis at which a leader of the St. Louis City police said that certain St. Louis County police departments treat minority residents so badly, City police have trouble getting cooperation from potential witnesses, impeding the City department’s ability to solve serious crimes.

    Robert Wilkins, now a federal appellate judge, was a plaintiff in 1990s litigation related to DWB stops in Maryland. A 2016 CBS News interview in which he describes his experiences is available here: [YouTube]

    In the spring and summer of 2020, police treatment of members of minority communities—especially African Americans—once again received a national spotlight. The May 2020 killing of George Floyd by police in Minneapolis and the March 2020 killing of Breonna Taylor by police in Louisville aroused particular indignation, inspiring protests across the country. Police response to protests in some cities, including violence captured on video, inspired further calls for reform, along with more radical proposals.

    As you read subsequent chapters, consider how Supreme Court criminal procedure decisions affect how police departments interact with communities they exist to serve. For example, does the Court’s Fourth Amendment doctrine encourage police officers to act in ways that build confidence among community members? When police officers violate rules set forth by the Court, do existing legal remedies encourage better future behavior? If you are unhappy with the state of policing, how might things be improved? If instead you think policing is going fairly well, to what do you attribute the discontent exhibited during the 2020 protests?

    One purpose of this book is to help you consider questions like these. Recall, however, that most Americans will never attend law school. Knowledge of criminal procedure doctrine among the public is sketchy at best. If Americans better understood Supreme Court doctrine related to the Fourth, Fifth, and Sixth Amendments, do you think they would have more or less faith in the criminal justice system? Why? After finishing this book, answer these questions again and examine whether your own opinions have changed.