What does a grand jury do in the U.S. criminal justice system?

In the U.S. criminal justice system, a grand jury is a group of laypersons tasked with determining whether there is sufficient evidence—known as "probable cause" or "prima facie evidence"—to believe a person has committed a crime.1

Key aspects of the grand jury's role include:

• Inquisitorial Function: Unlike a petit jury, which determines guilt or innocence at trial, a grand jury conducts an ex parte hearing where only the prosecution typically presents evidence. It does not decide if a defendant is guilty, but rather whether the government has enough evidence to proceed to trial.12
• Indictment: If the grand jury finds sufficient evidence, it issues an indictment, a formal accusation that requires the accused to stand trial.12
• Independence and Secrecy: While they work with prosecutors, grand juries operate with significant independence and secrecy. They have the power to subpoena witnesses and records to aid their investigation.1
• Constitutional Basis: The Fifth Amendment mandates grand jury indictments for federal capital or infamous crimes, though this requirement does not apply to state courts.132