What does a grand jury actually do?

A grand jury determines whether sufficient evidence exists to bring criminal charges, issuing an indictment if it finds probable cause. It is entirely separate from a trial jury, which decides guilt. Federal felony prosecutions require grand jury indictment under the Fifth Amendment, while states vary, with some using grand juries and others proceeding by prosecutor's information followed by a preliminary hearing before a judge. Grand juries are larger than trial juries, typically 16 to 23 members federally, and need only a majority rather than unanimity.

The procedural asymmetry is the defining feature. Proceedings are secret, the prosecutor presents the evidence without an opposing party, the defense attorney is not present, the target usually does not testify and has no right to present evidence, hearsay is generally admissible, and the judge does not preside. The standard is probable cause, far below beyond a reasonable doubt. The predictable result is that indictment rates are extremely high, which produced the well-known remark attributed to a New York judge that a prosecutor could get a grand jury to indict a ham sandwich.

Two functions beyond charging are worth knowing. Grand juries have substantial investigative power, including subpoenaing documents and compelling testimony, which makes them a tool for building complex cases against organized crime, corruption, and corporate wrongdoing. And secrecy serves real purposes: protecting the reputation of people investigated but not charged, preventing targets from fleeing or tampering with witnesses, and encouraging candid testimony. Critics argue the institution now functions largely as an extension of the prosecutor rather than as the independent check on charging power it was designed to be, and several states have reduced or eliminated its role for that reason.