Prosecutors play a pivotal role in the criminal justice and work closely with: law enforcement officials, judges, defense attorneys, probation and parole officers, victims services, human services, and to a lesser extent, with jail and other corrections officers. The authority to prosecute is divided among various city, state and federal officials. City and state officials are responsible for prosecutions under local and state laws, and federal officials for prosecutions under federal law. Associate Justice Robert Jackson, while he was the U.S. Attorney General addressed the Conference of United States Attorneys (federal prosecutors) in Washington, D.C. on April 1, 1940 and stated,
“The qualities of a good prosecutor are . . . [elusive and . . . impossible to define]. …
The prosecutor has more control over life, liberty, and reputation than any other person in America. His discretion is tremendous. He can have citizens investigated and, if he is that kind of person, he can have this done to the tune of public statements and veiled or unveiled intimations. Or the prosecutor may choose a more subtle course and simply have a citizen’s friends interviewed. The prosecutor can order arrests, present cases to the grand jury in secret session, and on the basis of his one-sided presentation of the facts, can cause the citizen to be indicted and held for trial. He may dismiss the case before trial, in which case the defense never has a chance to be heard. Or he may go on with a public trial. If he obtains a conviction, the prosecutor can still make recommendations as to sentence, as to whether the prisoner should get probation or a suspended sentence, and after he is put away, as to whether he is a fit subject for parole. While the prosecutor at his best is one of the most beneficent forces in our society, when he acts from malice or other base motives, he is one of the worst. …
Nothing better can come out of this meeting of law enforcement officers than a rededication to the spirit of fair play and decency that should animate the federal prosecutor. Your positions are of such independence and importance that while you are being diligent, strict, and vigorous in law enforcement you can also afford to be just. Although the government technically loses its case, it has really won if justice has been done. . . .
There is a most important reason why the prosecutor should have, as nearly as possible, a detached and impartial view of all groups in his community. Law enforcement is not automatic. It isn’t blind. One of the greatest difficulties of the position of prosecutor is that he must pick his cases because no prosecutor can even investigate all of the cases in which he receives complaints. If the department of justice were to make even a pretense of reaching every probable violation of federal law, ten times its present staff would be inadequate. We know that no local police force can strictly enforce the traffic laws, or it would arrest half the driving population on any given morning. What every prosecutor is practically required to do is to select the cases for prosecution and to select those in which the offense is the most flagrant, the public harm the greatest, and the proof the most certain.
… A sensitiveness to fair play and sportsmanship is perhaps the best protection against the abuse of power, and the citizen’s safety lies in the prosecutor who tempers zeal with human kindness, who seeks truth and not victims, who serves the law and not factional purposes, and who approaches his task with humility” 
State Prosecuting Attorneys
Prosecutors represent the citizens of the state, not necessarily a particular victim of a crime. States vary in how they organize the groups of attorneys hired to represent the state’s interest. Ordinarily, the official with the primary responsibility for prosecuting state violations is the local prosecutor who is referred to as the “district attorney”, “county attorney”, or “state’s attorney”. Local prosecutors are usually elected from a single county or a group of counties combined into a prosecutorial district. In many states, the state attorney general’s office has the authority that trumps over the local prosecutors’ authority, but in practice, the state attorney general rarely intervenes in local matters. The state attorney general’s office will intervene, for example, if there is a conflict of interest or when requested by the district attorney. It is not uncommon for a small local prosecutor’s office when faced with the prosecution of a major, complex, time-consuming trial, to request the aid of the attorney general’s office. In these smaller offices, there may be insufficient resources to handle complicated prosecutions and still keep up with the day-to-day filings and cases.
The prosecuting attorney and the attorney general ordinarily are the only officials with authority to prosecute violations of state law. City attorneys may be hired to prosecute city ordinances, but these attorneys primarily specialize in civil matters. When city attorneys and prosecuting attorneys have different policies for treating minor offenses, the result may be disparate, or different, treatment of similarly situated offenders. This raises a concern of inconsistent application of the law. Additionally, different county prosecutors may follow different policies on which matters they will charge, the use of diversion programs, the use of plea bargaining, and the use of certain trial tactics. To limit some of these differences, some states have used statewide training, and district attorneys’ conferences. Still, the policies and practices are far from uniform.
Generally, assistant prosecutors, called deputy district attorneys, are hired as “at will” employees by the elected district attorney. Historically, the political party of the applicant was a key criterion, and newly elected prosecutors would make a virtual clean sweep of the office and hire outsiders from the former office. Now, most offices hire on a non-partisan, merit-oriented, basis.
Most states require that the prosecutor be a member of the state bar. Some states also require that he or she have several years in the practice of law. Deputy district attorneys, on the other hand, are frequently fresh out of law school. They may have limited knowledge of state criminal law, as law school is designed to teach lawyers to enter any new field and educate themselves.
Link to the Oregon District Attorneys Association Website https://www.oregonda.org/
Federal Prosecuting Attorneys
Prosecutors in the federal system are part of the U.S. Department of Justice and work under the Attorney General of the United States. The Attorney General does not supervise individual prosecutors and relies on the 94 United States Attorneys, one for each federal district. U.S. Attorneys are given considerable discretion, but they must operate within general guidelines prescribed by the Attorney General. The U.S. Attorneys have a cadre of Assistant U.S. Attorneys who do the day-to-day prosecution of federal crimes. For certain types of cases, approval is needed from the Attorney General or the Deputy Attorney General in charge of the Criminal Division of the Department of Justice. The Criminal Division of the Department of Justice (DOJ) operates as the arm of the Attorney General in coordinating the enforcement of federal laws by the U.S. Attorneys.
Link to cite to find the U.S. Attorney https://www.justice.gov/usao/find-your-united-states-attorney
Selection and Qualifications of Prosecutors
Most local prosecuting attorneys are elected in a partisan election in the district they serve. State attorney generals may also have significant prosecutorial authority. They are elected in forty-two states, appointed by the governor in six states, appointed by the legislature in one state, and appointed by the state supreme court in another. State attorney generals serve between two to six-year terms, which can be repeated. Federally, senators from each state recommend potential U.S. Attorney nominees who are then appointed by the President with the consent of the Senate. U.S. Attorneys tend to be of the same political party as the President and are usually replaced when a new President from another party takes office.
Prosecutors arguably have more discretion than any other official in the criminal justice system. They decide whether to charge an individual or not. Much has been written about the prosecutor’s broad discretion and the constraints on his or her discretion. If they choose not to prosecute, this is referred to as nolle prosequi, and this decision is largely unreviewable. Spohn and Hemmens (2012, p. 123) concluded in their review of the studies on prosecutor’s charging decisions that “these highly discretionary and largely invisible decisions reflect a mix of (1) legally relevant measures of case seriousness and evidence strength and (2) legally irrelevant characteristics of the victim and the suspect” .
Prosecutors guide the criminal investigation and work with law enforcement to procure search and arrest warrants. Following arrest, prosecutors continue to be involved with various aspects of the investigation. Roles include: meet with the arresting officers, interview witnesses, visit the crime scene, review the physical evidence, determine the offenders prior criminal history, make bail and release recommendations, appear on pretrial motions, initiate plea negotiations, initiate diversions (pre-trial contracts between the government and the defendant which divert cases out of the system), work with law enforcement officers from other states who seek to extradite offenders, prepare the accusation to present to grand jury, call witnesses and present a prima facia case (present enough evidence which, when unrebutted by the defendant, shows that the defendant committed the crime) at a preliminary hearing, represent that state at arraignments and status conferences, conduct the trial, and, upon conviction, make sentencing recommendations while representing the state at the sentencing hearing.
In many communities, the prosecutor is the spokesperson for the criminal justice system and appears before the legislature to recommend or oppose penal reform. Prosecutors make public speeches on crime and law enforcement, take positions on requests for clemency for cases they have prosecuted, work extensively with victims’ services offices, which may be an arm of the prosecutor’s office. In some communities, the prosecutor is also responsible for representing the local government in civil matters and may represent the state in civil commitment proceedings and answer accident claims, contract claims, and labor relation matters for the county. However, only a few counties have prosecutors still perform this function. U.S. Attorneys still have substantial responsibilities for representation of the U.S. government in civil litigation, and there is generally a civil division, a criminal division, and an appellate division of the U.S Attorneys office.
The American Bar Association (ABA) standards indicate that “the prosecutor’s [ethical] duty is to seek justice”. This means that the state should not go forward with prosecution if there is insufficient evidence of the defendant’s guilt or if the state has “unclean hands”, for example, illegally conducted searches or seizures or illegally obtained confessions. Ethical and disciplinary rules of the state bar associations govern prosecutors who must also follow state and constitutional directives when they prosecute crimes.
Link to the ABA Standards on the Prosecution Function https://www.americanbar.org/groups/criminal_justice/standards/ProsecutionFunctionFourthEdition-TableofContents/