起訴とは何か、どのように機能するのか？

What Is Prosecution and How Does It Work? - LegalClarity Criminal Law What Is Prosecution and How Does It Work? Learn how criminal prosecution works, from charges and arraignment through trial, plea deals, and sentencing. LegalClarity Team Published Mar 8, 2026 Prosecution is the process by which a government brings and pursues criminal charges against a person or organization accused of breaking the law. Rather than leaving individuals to seek justice on their own, the state takes on the responsibility of investigating alleged crimes, filing formal charges, and presenting evidence in court. The prosecutor represents the public interest, not any particular victim, which means a case can move forward even if the victim doesn’t want to participate. Understanding how prosecution works helps clarify what happens between an arrest and a verdict, and where constitutional protections come into play at each stage. Key Participants in a Criminal Prosecution A criminal case revolves around three main figures: the prosecutor, the defendant, and the judge. At the federal level, U.S. Attorneys are responsible for prosecuting crimes within their assigned districts. 1 United States Code. 28 USC 547 – Duties State and local cases are handled by district attorneys, county prosecutors, or state attorneys general, depending on the jurisdiction. These lawyers represent “the People” or “the State,” not the individual victim. That distinction matters because it means the prosecutor’s job is to enforce the law fairly, not to win at all costs on behalf of one person. The defendant is the person or organization facing criminal charges. The Sixth Amendment guarantees every criminal defendant the right to an attorney, and if the defendant can’t afford one, the court must appoint counsel. The defendant doesn’t have to prove anything. The entire burden of proving guilt falls on the government. The judge acts as a referee. Judges rule on what evidence the jury can hear, resolve legal disputes between the prosecution and defense, and ensure the proceedings follow the rules. In cases where a defendant is found guilty, the judge determines the sentence , weighing factors like the severity of the offense, the defendant’s criminal history, and any aggravating or mitigating circumstances. Where Victims Fit In Crime victims are not parties to the case the way the government and defendant are. A victim doesn’t file or control the prosecution. That said, federal law gives victims specific rights, including the right to notice of court proceedings, the right to attend those proceedings, and the right to be heard at key stages like bail hearings, plea hearings, and sentencing. The prosecutor must also inform the victim of any plea bargain or agreement to defer prosecution . 2 United States Code. 18 USC 3771 – Crime Victims Rights Most states have adopted similar protections. Prosecutorial Discretion One of the most powerful and least visible parts of the prosecution process happens before a case ever reaches a courtroom. Prosecutors decide whether to file charges, what charges to bring, and whether to offer a plea deal. This authority, known as prosecutorial discretion , has no single statute spelling it out. It’s an inherent feature of the executive branch’s law enforcement power, and courts give prosecutors wide latitude in exercising it. In practice, this means a prosecutor can review the evidence after an arrest and decide the case isn’t strong enough to pursue, that the offense is better handled through a diversion program , or that the facts support a more serious charge than what police originally recommended. A prosecutor can also file a motion to dismiss charges already on the docket. While judges can accept or reject plea agreements, they generally can’t force a prosecutor to bring or maintain charges. 3 Congress.gov. Federal Prosecutorial Discretion – A Brief Overview This is where most of the real leverage in the criminal system lives, and it’s the reason two people arrested for similar conduct can end up facing very different charges. How a Prosecution Begins Before a case goes to trial, the government has to clear several procedural hurdles. The process starts with establishing probable cause , which means enough evidence exists for a reasonable person to believe a crime was committed and the defendant committed it. From there, the government formalizes the charges through one of two documents: an information (filed directly by the prosecutor) or an indictment (returned by a grand jury) . Grand Juries and Indictments The Fifth Amendment requires a grand jury indictment for serious federal crimes. 4 Legal Information Institute. Fifth Amendment This requirement applies only in federal court; states can choose whether to use grand juries or let prosecutors file charges directly. A federal grand jury has between 16 and 23 members, and at least 12 must agree before an indictment can issue. 5 Legal Information Institute. Federal Rules of Criminal Procedure Rule 6 – The Grand Jury Grand jury proceedings are secret. Only the prosecutor presents evidence, and the defendant has no right to appear or cross-examine witnesses. If the grand jury finds sufficient evidence, it returns what’s called a “ true bill ,” which becomes the formal indictment. It’s worth noting that the grand jury’s role is limited. The standard is probable cause, not proof beyond a reasonable doubt. Grand juries are sometimes called a “sword” rather than a “shield” because they almost always return indictments. The constitutional function of grand juries in federal courts is to return criminal indictments, and the Fifth Amendment’s grand jury requirement has never been extended to the states through the Fourteenth Amendment. 6 LII / Legal Information Institute. Grand Jury Clause Doctrine and Practice Initial Appearance and Arraignment After a person is arrested or charged, they must be brought before a judge without unnecessary delay. 7 Legal Information Institute. Federal Rules of Criminal Procedure Rule 5 – Initial Appearance At this initial appearance , the judge informs the defendant of the charges, advises them of their right to an attorney, and decides whether to release or detain them pending trial. The defendant doesn’t enter a plea at this stage in felony cases. The plea comes at arraignment , which is a separate proceeding. At arraignment, the court ensures the defendant has a copy of the indictment or information, reads the charges or explains them, and asks the defendant to enter a plea. 8 Legal Information Institute. Federal Rules of Criminal Procedure Rule 10 – Arraignment Most defendants plead not guilty at this point, even if they later negotiate a deal. A not-guilty plea simply triggers the timeline for trial preparation. Statute of Limitations The government can’t wait forever to bring charges. For most federal crimes, the statute of limitations is five years from the date the offense was committed. 9 United States Code. 18 USC 3282 – Offenses Not Capital If the government doesn’t file an indictment or information within that window, the prosecution is barred. Capital offenses — crimes punishable by death — have no statute of limitations at all. 10 United States Department of Justice Archives. Criminal Resource Manual 650 – Length of Limitations Period Many specific federal crimes carry their own limitations periods that override the general five-year rule. Tax evasion, for instance, has a six-year window. Certain terrorism and fraud offenses have even longer periods. State limitations periods vary widely, though murder typically has no time limit in any state. The clock usually starts when the crime is committed, not when it’s discovered, although some fraud-based offenses use a discovery rule that extends the deadline. The Speedy Trial Requirement Beyond the statute of limitations, the Speedy Trial Act sets hard deadlines once a prosecution is underway. The government must file an indictment or information within 30 days of the defendant’s arrest, and the trial must begin within 70 days after the indictment is filed or the defendant first appears before the court, whichever comes later. 11 Office of the Law Revision Counsel. 18 USC 3161 – Time Limits and Exclusions Those deadlines sound tight, and they are — but the statute includes a long list of excludable delays, such as time for pretrial motions, competency evaluations, and interlocutory appeals. In practice, complex federal cases routinely take months or years to reach trial without violating the Act. If the deadlines are missed without a valid exclusion, however, the charges must be dismissed. Plea Bargaining The vast majority of criminal cases never go to trial. Researchers estimate that 90 to 95 percent of both federal and state cases are resolved through plea bargaining. 12 Bureau of Justice Assistance. Plea and Charge Bargaining Research Summary In a plea bargain, the defendant agrees to plead guilty (usually to a reduced charge or in exchange for a lighter sentencing recommendation) and the government avoids the cost, risk, and delay of a trial. Plea agreements must be disclosed in open court, and the judge must verify that the defendant understands the rights being waived, including the right to a jury trial, the right to confront witnesses, and the privilege against self-incrimination . The judge also confirms that the plea is voluntary and not the result of threats or promises outside the agreement. A judge can reject a plea deal, though this is uncommon. When the deal involves the government dropping other charges, courts give deference to the prosecutor’s judgment but aren’t required to rubber-stamp the arrangement. 3 Congress.gov. Federal Prosecutorial Discretion – A Brief Overview The Prosecutor’s Disclosure Obligations Prosecutors have a constitutional duty to play fair with evidence. Under the rule established in Brady v. Maryland , the government must turn over any evidence that is fav