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7.1: Criminal Defenses – General Principles

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    Our collective human experience recognizes that most individuals engage in criminal behavior for a reason, be it anger, survival, greed, mental illness, desire, or fear. Some reasons are acceptable, some are not. Over the next two chapters, we will explore when a reason legally excuses or legally justifies criminal behavior.

    Recall that the American criminal legal system is based on the presumption of innocence. All criminal defendants are presumed innocent of the crime charged. The presumption remains unless the government can prove the defendant guilty beyond a reasonable doubt. See In re Winship, 397 U.2. 364 (1970). This burden applies to every essential element of the crime. If the government fails to establish the defendant’s guilt beyond a reasonable doubt, the trier of fact must acquit the defendant. Due process demands the government carry this burden through the entire trial; the burden of proof never shifts to the defendant.

    Since a criminal defendant is never required to prove their innocence, a defendant is permitted to simply sit back and wait for the prosecution to meet its burden of proof. The government’s failure to meet its burden of proof is sometimes referred to as a failure of proof defense. The next two chapters focus on a different type of defense – those criminal defenses in which the defendant affirmatively denies the charge due to the existence of a non-constitutional, statutorydefense.[1] In fact, most criminal defenses are statutory, and because of this there is little overlap between jurisdictions. Although most states authorize similar defenses to criminal conduct, individual legislatures frequently limit or expand the availability of a particular defense depending on the desires of the electorate. The next two chapters explore criminal defenses applicable in Alaska.

    Some Evidence

    Although a defendant is always permitted to sit back and force the government to prove its case beyond a reasonable doubt, a defendant may only raise a defense if there is a factual basis to do so. The law requires a defendant to present “some evidence” of a defense (affirmative or otherwise) before the jury may consider it. “Some evidence” is a term of art, and typically means “there is evidence from which a reasonable juror could entertain a reasonable doubt as to the defendant’s guilt.” See Weston v. State, 682 P.2d 1119, 1121 (Alaska 1984). It is not a high burden; it is designed to ensure that the jury focuses on the relevant facts during trial, and not waste its time on interesting but largely irrelevant factual disputes.

    Example of Not Establishing Some Evidence

    Jim is on trial for the murder of Fred. According to the government, Jim and Fred have a long-standing hatred toward each other. On the night of the homicide, the government alleges that Jim walked up to Fred’s house, rang the doorbell, and waited for Fred to answer the door. As the door swung open, Jim shot Fred in the chest at point-blank range, killing him instantly. The government alleges that the murder was recorded on Fred’s home surveillance camera system. Jim claims he did not kill Fred and argues that the video recording of the murder is too pixelated to clearly make out who shot Fred. Jim intends to rely on the government’s inability to prove his identity beyond a reasonable doubt. Under this scenario, Jim would not be entitled to argue he shot Fred in self-defense. There is no evidence, nor is there any reasonable interpretation of the evidence, that would justify a reasonable juror to believe Jim was justified in killing Fred.

    Categorization of Criminal Defenses

    Not all criminal defenses operate in the same manner. Some must be disproven by the government (a defense), while others must be proven by the defendant (an affirmative defense). Some completely exonerate the defendant of criminal wrongdoing (e.g., perfect defense), while others simply reduce the severity of the offense (e.g., imperfect defense). Some defenses are questions of law (a legal defense), while others are issues of fact (a factual defense).

    Defense versus Affirmative Defense

    Most legislatures classify criminal defenses as either a “defense” or “affirmative defense.” The law treats defenses as the equivalent of an element of the crime, requiring the government to disprove the defense beyond a reasonable doubt. AS 11.81.900(19). An affirmative defense, on the other hand, operates independently of the government’s burden of proof. Unlike a defense, an affirmative defense must be proven by the defendant by a preponderance of the evidence. AS 11.81.900(b)(2). It is the defendant’s burden to prove an affirmative defense.

    Example of an Affirmative Defense

    Remember Matthew, Melissa, and the neighbor’s pesky dog from the last chapter? Melissa purchased rat poison and Matthew covered a filet mignon with it, with the intent to kill the neighbor’s pesky pet. After Matthew threw the filet over the fence, Melissa changed her mind. She climbed over the fence, picked up the filet, and took it back to her house for disposal. Melissa sought to avoid criminal liability for attempted animal cruelty using the affirmative defense of renunciation. Because renunciation is an affirmative defense, Melissa bears the burden of proving its existence – that is, Melissa must prove, by a preponderance of the evidence, that she freely and voluntarily abandoned her intent to harm the dog and that she took steps to prevent the crime. The government need not prove any of the elements of renunciation.

    Justification and Excuse

    Most criminal defenses are categorized as either a justification defense or an excuse defense. A defendant who relies on a justification defense is asserting that his behavior was legally justified. The underlying principle is that the harm avoided by the defendant’s conduct far outweighs the harm caused by the defendant’s conduct. Put another way, with a justification defense, society is affirmatively condoning the defendant’s conduct. A defendant who relies on an excuse defense is not claiming they were justified in their actions, but claiming that they should not be held responsible for their actions because of a circumstance that prevented them from acting lawfully. In other words, with an excuse defense, the defendant is asking the trier of fact to excuse their criminal conduct based on a unique condition that prevented them from acting lawfully. Common criminal defenses are categorized as either justification or excuse below:

    Justification Defenses Excuse Defenses
    Self-defense / Defense of others Insanity
    Defense of property Infancy
    Duress Voluntary intoxication
    Necessity Heat of passion

    Perfect versus Imperfect Defenses

    A closely related concept is the difference between perfect and imperfect defenses. A criminal defense that completely exonerates a defendant of a crime is referred to as a perfect defense. Self-defense is a common perfect defense. A criminal defendant who successfully proves they acted in self-defense is relieved of all criminal liability surrounding the original criminal conduct. Conversely, an imperfect defense simply reduces the severity of the defendant’s criminal conduct. Heat-of-passion is an imperfect defense in Alaska. A defendant who successfully proves they killed under a heat of passion still stands convicted of homicide, albeit a lower classification, manslaughter. The difference between the two is significant – a perfect defense results in an acquittal, whereas an imperfect defense results in a conviction for a less serious offense.

    Definition of Factual and Legal Defenses

    A defense must be based on specific grounds. If a defense is based on an issue of fact, it is a factual defense. If a defense is based on an issue of law, it is a legal defense.

    Example of Factual and Legal Defenses

    Armando is charged with the burglary of Roman’s residence. Armando decides to pursue two defenses. First, Armando claims that it was 35 degrees below zero on the night of the burglary and he broke into Roman’s residence to avoid freezing to death. This is called the defense of necessity and is a factual defense; it is based on the fact that Armando faced a bona fide emergency and committed the burglary to avoid a greater harm. Second, Armando claims that the government is prohibited from prosecuting him for burglary because the statute of limitations has expired. A statute of limitations defense is a legal defense because it is based on a statute that requires the government to bring all criminal prosecutions within a specified timeframe.


    1. We have previously explored various constitutional defenses to criminal law enforcement. For example, both the U.S. and Alaska constitution prohibits criminal punishment from being applied retroactively. If a law attempts to punish conduct that was not criminal at the time it was committed, the ex post facto clause would operate as a constitutional defense to any criminal charge. We will now focus on statutorily created defenses, which normally exist independent of the constitution.

    This page titled 7.1: Criminal Defenses – General Principles is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rob Henderson via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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