The grand jury exists for two reasons: the Fifth Amendment requires one before the federal government can prosecute a serious crime, and prosecutors need its investigative powers, especially the subpoena, to build cases that would otherwise be impossible to make. Asking why we use a grand jury is really asking two questions at once, one constitutional and one practical, and the answers pull in different directions. The constitutional purpose is to put a buffer of ordinary citizens between the accused and the government. The practical purpose is to give prosecutors a closed, one-sided forum with real legal muscle behind it.
The Constitutional Reason
The Fifth Amendment says that no person “shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury.”1Congress.gov. Fifth Amendment – Constitution of the United States In practice, “infamous crime” has been read to cover all federal felonies. Before the government can put someone through a criminal trial, 16 to 23 citizens with no stake in the outcome have to agree there is enough evidence to justify it. That civilian check is the original idea of the grand jury, and it is why one exists at all in federal cases.
This requirement is federal only. In Hurtado v. California (1884), the Supreme Court held that the Fourteenth Amendment does not force the grand jury requirement onto the states.2Justia Law. Hurtado v California, 110 US 516 (1884) About half the states use grand juries for serious felonies anyway. The rest let prosecutors charge by “information,” a document filed directly with the court that skips the grand jury entirely.3Constitution Annotated. Grand Jury Clause Doctrine and Practice So if you are wondering why a state case near you did not go to a grand jury, that is the reason: the Constitution does not require it, and that state did not choose to.
The Investigative Reason
The grand jury is not only a screening body. It is also an investigative one, and that is the part prosecutors care about most in complex cases involving financial fraud, public corruption, or organized crime, where the evidence is buried in records and the witnesses do not want to talk.
The key tool is the grand jury subpoena, governed in federal court by Rule 17 of the Federal Rules of Criminal Procedure.4U.S. Department of Justice. Justice Manual 9-11.000 – Grand Jury A subpoena can compel a witness to appear and testify under oath. It can also force a person or company to turn over documents, financial records, or other physical evidence. Without the grand jury, prosecutors have no comparable way to reach information that no one is willing to hand over voluntarily.
Refusing to comply has teeth. Under 28 U.S.C. 1826, a witness who refuses can be held in civil contempt and confined until they cooperate. The confinement cannot last past the end of the grand jury’s term, and it cannot run longer than 18 months in any event.5Office of the Law Revision Counsel. 28 USC 1826 – Recalcitrant Witnesses This is coercive, not punitive. The witness holds the key: agree to testify or produce the materials, and the confinement ends.
Why Not Just Use a Preliminary Hearing
Where grand jury indictment is not required, the usual alternative is a preliminary hearing. Both proceedings answer the same question, which is whether probable cause exists to send a case to trial. They answer it in very different ways.
A grand jury is one-sided. Only the prosecutor presents evidence. There is no judge in the room. The defense has no role at all. A preliminary hearing is the opposite: open court, a judge presiding, defense counsel present, cross-examination of the government’s witnesses, and sometimes defense evidence of its own. For a defendant, the preliminary hearing is a far better deal, because it is an early, public look at the government’s case with a chance to push back. For a prosecutor running a sensitive investigation, the grand jury is the better deal, because the case can be built without tipping off anyone the government is not ready to charge.
That trade-off is the practical answer to “why use a grand jury.” It lets prosecutors investigate quietly, lock witnesses into sworn testimony, and gather records, all before the defense knows what is coming.
Secrecy and Who Is in the Room
Grand jury proceedings are closed. Federal Rule of Criminal Procedure 6 identifies exactly who is bound by the secrecy obligation: the grand jurors, interpreters, court reporters, operators of recording devices, transcribers, and government attorneys.6Legal Information Institute. Federal Rules of Criminal Procedure Rule 6 – The Grand Jury Witnesses are not on that list. A witness who testifies before a federal grand jury is free to talk about their own testimony afterward.
Only a few people are inside while the panel is in session: the government’s lawyers, the witness being questioned, an interpreter if needed, and a court reporter.6Legal Information Institute. Federal Rules of Criminal Procedure Rule 6 – The Grand Jury No judge. No defendant. No defense attorney. A witness can have a lawyer available, but in federal practice that lawyer waits outside. If the witness wants advice during questioning, they have to leave the room to get it. Secrecy protects the investigation while it is active and protects the reputations of people who are looked at but never charged.
Does the Check Actually Work
After hearing the evidence, the grand jury votes. The standard is probable cause, which means enough evidence to create a reasonable belief that a crime occurred and that the target committed it. It is well below the “beyond a reasonable doubt” standard that applies at trial.7United States Courts. Types of Juries If at least 12 jurors agree, the panel returns an indictment, also called a “true bill,” and the case moves forward. Fewer than 12 produces a “no bill,” and the charges do not go anywhere.6Legal Information Institute. Federal Rules of Criminal Procedure Rule 6 – The Grand Jury
In theory, that vote is a meaningful check on an overreaching prosecutor. In practice, federal grand juries almost always indict. Bureau of Justice Statistics data from recent years shows federal grand juries declining to indict in fewer than two dozen cases out of more than 150,000 matters per year. The imbalance prompted former New York Chief Judge Sol Wachtler’s often-quoted line that a prosecutor could get a grand jury to “indict a ham sandwich.” The one-sided structure explains most of it. The prosecutor picks the witnesses, frames the evidence, and answers the jurors’ legal questions, and the defense is nowhere in the room.
So the honest answer to why we use a grand jury has two parts. The constitutional answer is that the Fifth Amendment demands a citizen check before the federal government can prosecute a felony. The working answer is that the grand jury gives prosecutors a secret, controlled forum with subpoena power behind it. Both answers are true. They just do not sit comfortably next to each other.