検察官は法廷で何をするのか：起訴から裁判まで

What Does a Prosecutor Do in Court: From Charges to Trial - LegalClarity Criminal Law What Does a Prosecutor Do in Court: From Charges to Trial Prosecutors do more than argue in court — they shape cases from the grand jury stage through sentencing, balancing justice with advocacy. LegalClarity Team Published Apr 1, 2026 A prosecutor’s core duty in court is to seek justice on behalf of the public, not simply to rack up convictions. As a government attorney representing the state or federal government in criminal proceedings, a prosecutor carries the burden of proving guilt beyond a reasonable doubt while simultaneously ensuring the process stays fair for the defendant. Roughly 90 to 95 percent of criminal cases resolve through plea bargains rather than trials, so much of a prosecutor’s courtroom work happens long before anyone delivers an opening statement. The Duty to Seek Justice Every other duty a prosecutor performs flows from one foundational obligation: the pursuit of justice rather than victory. The U.S. Supreme Court spelled this out in 1935, stating that a prosecutor “is the representative not of an ordinary party to a controversy, but of a sovereignty whose obligation to govern impartially is as compelling as its obligation to govern at all.” The Court emphasized that the government’s interest in a criminal case “is not that it shall win a case, but that justice shall be done.” 1 Library of Congress. Berger v. United States, 295 U.S. 78 (1935) In practical terms, this means a prosecutor can and should advocate aggressively for the government’s case, but cannot use improper methods to get a conviction. Professional conduct rules adopted in virtually every state spell out specific guardrails: a prosecutor cannot file charges unsupported by probable cause , cannot try to obtain waivers of important rights from defendants who have no lawyer, and must turn over evidence that helps the defense . These aren’t suggestions. Violating them can lead to disciplinary action, case dismissal, or overturned convictions. Grand Jury Proceedings and Charging Before a case reaches a courtroom for trial, someone has to decide whether formal charges are warranted. For serious federal crimes and in many states, that decision runs through a grand jury. The prosecutor presents evidence to a panel of citizens who then decide whether probable cause exists to issue an indictment . Unlike a trial jury, the grand jury hears only the prosecutor’s side — the defendant generally has no right to appear, present evidence, or even have an attorney in the room. The prosecutor’s influence in this setting is enormous. The grand jury relies on the prosecutor to explain the law, present witnesses, and guide the proceeding. In most states, prosecutors who possess strong, credible evidence pointing toward innocence must share it with the grand jury. Federal prosecutors, however, have no such obligation — the reasoning being that the defendant will have a full opportunity to present exculpatory evidence at trial. Not every criminal charge goes through a grand jury. In many state systems, prosecutors can file charges directly through a document called an information , which typically follows a preliminary hearing where a judge independently evaluates whether probable cause exists. Disclosing Evidence to the Defense One of the most consequential duties a prosecutor carries is the obligation to hand over evidence favorable to the defendant. The Supreme Court established this requirement in 1963, holding that withholding evidence that is material to guilt or punishment violates due process — regardless of whether the prosecutor acted in bad faith. 2 United States Department of Justice. Policy Regarding Disclosure of Exculpatory and Impeachment Information This disclosure duty extends beyond evidence that directly proves innocence. Prosecutors must also turn over material that could be used to undermine the credibility of government witnesses — things like a cooperating witness’s plea deal, prior inconsistent statements, or evidence that a law enforcement officer has a history of dishonesty. Department of Justice policy requires prosecutors to take a broad view of what qualifies and to err on the side of disclosure. The obligation kicks in regardless of whether the defense asks for the material, and it continues throughout the case: if new favorable evidence surfaces mid-trial, the prosecutor must disclose it promptly. 2 United States Department of Justice. Policy Regarding Disclosure of Exculpatory and Impeachment Information Formal Discovery Obligations Beyond the constitutional duty to disclose favorable evidence, federal rules require prosecutors to share a broad range of case materials once the defense requests them. This includes the defendant’s own recorded statements, prior criminal history, documents and physical items the government plans to use at trial, and results of any examinations or tests. For expert witnesses, the prosecutor must provide written summaries of the expert’s expected opinions, the reasoning behind them, and the expert’s qualifications — all sufficiently before trial to give the defense a fair chance to respond. 3 Legal Information Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection These disclosure obligations are ongoing. If the prosecutor discovers additional material before or during trial that falls within the scope of what was requested, the rules require prompt disclosure. Prosecutors do retain protection over internal work product — notes, legal strategy memos, and other documents created in connection with investigating the case — but the line between protected strategy and disclosable evidence is one that courts scrutinize closely. Pre-Trial Court Appearances A prosecutor’s courtroom duties begin well before trial. The earliest is typically the arraignment , where the defendant appears before a judge, hears the formal charges, and enters a plea. The prosecutor presents those charges and provides the court with a factual summary supporting them. Bail hearings follow shortly after. The prosecutor may argue that a defendant should remain in custody — presenting evidence of flight risk, danger to the community, or the seriousness of the charges — or may agree to release with conditions like electronic monitoring or no-contact orders with victims. The prosecutor’s recommendation carries weight, but the judge makes the final call. Pre-trial motions consume significant courtroom time. The defense often files motions to suppress evidence , arguing that police obtained it through an illegal search or coerced confession. When that happens, the prosecutor must defend the legality of the evidence collection, presenting testimony from officers and arguing that constitutional requirements were met. 4 National Institute of Justice. Law 101 – Legal Guide for the Forensic Expert – Motion to Suppress Losing a suppression motion can gut a case, so this is often where the real fight happens. Negotiating and Presenting Plea Agreements Given that the vast majority of criminal cases never reach trial, plea bargaining is arguably the duty prosecutors exercise most frequently. A plea agreement is a negotiated deal where the defendant agrees to plead guilty — usually to a reduced charge or in exchange for a sentencing recommendation — rather than going to trial. Federal rules outline three basic types of concessions a prosecutor can offer in a plea deal: agreeing to drop other charges, recommending a particular sentence (which the judge can accept or reject), or agreeing to a specific sentence that binds the court once accepted. 5 Legal Information Institute. Federal Rules of Criminal Procedure Rule 11 – Pleas The judge is excluded from the negotiations themselves but plays a critical role once a deal is reached. When a defendant enters a guilty plea, the prosecutor participates in the plea colloquy — the in-court proceeding where the judge confirms that the plea is knowing and voluntary. The court must find a factual basis for the plea, and it can satisfy that requirement by questioning the prosecutor about the evidence. The plea agreement must be disclosed in open court, and if the judge rejects the deal, the defendant gets the chance to withdraw the plea. 5 Legal Information Institute. Federal Rules of Criminal Procedure Rule 11 – Pleas Selecting the Jury When a case does go to trial, the prosecutor’s first task in the courtroom is helping select the jury through a process called voir dire . The prosecutor and defense attorney question a pool of potential jurors, looking for biases or experiences that would prevent someone from evaluating the evidence fairly. A prosecutor might ask whether a juror has personal connections to law enforcement, prior experience with the criminal justice system, or exposure to media coverage of the case. Both sides can remove jurors in two ways. Challenges for cause — where a lawyer argues that a specific juror cannot be impartial — have no numerical limit but require the judge’s approval. Peremptory challenges let each side remove jurors without stating a reason, but the number is capped. In federal cases, the government gets 20 peremptory challenges in capital cases, 6 in other felony cases, and 3 in misdemeanor cases. 6 Legal Information Institute. Federal Rules of Criminal Procedure Rule 24 – Trial Jurors Peremptory challenges come with one major restriction: prosecutors cannot use them to strike jurors based on race. If the defense raises a challenge alleging racial discrimination, the burden shifts to the prosecutor to provide a race-neutral explanation for the strike. The judge then decides whether the explanation is genuine or a pretext for discrimination. 7 United States Courts. Facts and Case Summary – Batson v. Kentucky This protection has expanded over the years to cover gender and other characteristics as well. Presenting the State’s Case Trial begins with the