大陪審
In criminal law in federal courts and a minority of state court systems of the United States, a grand jury is convened to hear only testimony and evidence to determine whether there is a sufficient basis for deciding to indict the defendant and proceed toward trial. In each court district where a grand jury is required, a group of 16–23 citizens holds an inquiry on criminal complaints brought by the prosecutor to decide whether a trial is warranted (based on the standard that probable cause exists that a crime was committed), in which case an indictment is issued. In jurisdictions where the size of a jury varies, in general the size of juries tends to be larger if the crime alleged is more serious. If a grand jury rejects a proposed indictment the grand jury's action is known as a "no bill." If they accept a proposed indictment, the grand jury's action is known as a "true bill." Grand jury proceedings are "ex parte": only the prosecutor and witnesses who the prosecutor calls may present evidence to the grand jury and defendants are not allowed to present mitigating evidence or even to know the testimony that was presented to the grand jury, and hearsay evidence is permitted. This is so because a grand jury cannot convict a defendant. It can only decide to indict the defendant and proceed forward toward trial. Grand juries vote to indict in the overwhelming majority of cases, and prosecutors are not prohibited from presenting the same case to a new grand jury if a "no bill" was returned by a previous grand jury. A typical grand jury considers a new criminal case every fifteen minutes. In some jurisdictions, in addition to indicting persons for crimes, a grand jury may also issue reports on matters that they investigate apart from the criminal indictments, particularly when the grand jury investigation involves a public scandal. Historically, grand juries were sometimes used in American law to serve a purpose similar to an investigatory commission.