The Fifth Amendment provides 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. That requirement, implemented by Federal Rule of Criminal Procedure 6 and 7, is why every federal felony prosecution begins with a grand jury unless the defendant waives indictment and consents to proceed by information.

Composition and mechanics

A federal grand jury has 16 to 23 members drawn from the district's jury wheel. Sixteen constitutes a quorum, and twelve concurring votes are required to return an indictment — a "true bill." A refusal to indict is a "no bill." Regular grand juries sit for up to 18 months, and a special grand jury convened for a long-running investigation may sit for 18 months with extensions up to 36.

Grand jurors do not sit daily. They convene periodically, hear evidence in multiple unrelated matters, and vote on charges presented by assistant United States attorneys. The proceeding takes place in a room in the courthouse with no judge present.

Two functions, not one

The screening function is the constitutional one: standing between the government and the citizen by requiring an independent body to find probable cause before a person is put to trial. Probable cause is a low standard — considerably lower than proof beyond a reasonable doubt — and the grand jury hears only what the prosecutor presents.

The investigative function is the one that matters more in practice. The grand jury's subpoena power reaches documents (a subpoena duces tecum) and testimony (a subpoena ad testificandum) nationwide. It compels bank records, corporate files, medical records, phone records, and testimony under oath from witnesses who would otherwise decline to speak to agents. Prosecutors use that power to build cases long before any charging decision is made.

What is absent from the room

  • No judge. A district judge supervises the grand jury and rules on subpoena disputes and contempt, but does not preside over the presentation.
  • No defense counsel. A witness's attorney may not enter the grand jury room. The witness may leave to consult counsel in the hallway.
  • No cross-examination and no defense evidence. The target has no right to testify, no right to present witnesses, and no right to have exculpatory evidence presented. In United States v. Williams (1992), the Supreme Court held that a prosecutor has no constitutional obligation to present exculpatory evidence to a grand jury, though the Justice Manual directs prosecutors to disclose substantial exculpatory evidence as a matter of internal policy.
  • Largely no rules of evidence. In Costello v. United States (1956), the Court held an indictment may rest entirely on hearsay. Agents routinely summarize an investigation rather than calling percipient witnesses.

Secrecy

Rule 6(e) imposes secrecy on grand jurors, prosecutors, agents, interpreters, and court reporters. Witnesses are not bound by it and may discuss their own testimony. The rule's purposes are to prevent flight, protect grand juror deliberations from pressure, prevent witness tampering, and protect the reputations of people investigated but never charged. Disclosure of grand jury material outside the narrow exceptions in Rule 6(e)(3) — including to a court in specified circumstances — requires judicial authorization.

Secrecy is also why so little is publicly knowable about an ongoing federal investigation. The absence of news is not evidence that nothing is happening.

The grand jury's power is not the power to accuse. It is the power to compel.

Witnesses, immunity, and the privilege

A witness before a grand jury testifies under oath and may invoke the Fifth Amendment privilege against self-incrimination question by question. A corporation has no such privilege, and under the collective entity doctrine a records custodian cannot refuse to produce corporate documents on personal Fifth Amendment grounds.

Where a witness invokes, the government may seek use immunity under 18 U.S.C. §§ 6002-6003, which bars use of the compelled testimony and anything derived from it, but does not bar prosecution based on independent evidence. A witness immunized in this way can be held in contempt for continued refusal to answer. False testimony exposes the witness to perjury liability under 18 U.S.C. § 1623 regardless of immunity.

The critique, and why it persists

The oft-quoted line that a grand jury would "indict a ham sandwich" reflects a real asymmetry: no-bills are rare, and the proceeding is entirely controlled by the prosecutor. Defenders of the institution respond that its screening role is modest by design and that the meaningful adversarial testing occurs at trial and on pretrial motions. Both are true. For anyone whose conduct is under grand jury scrutiny, the operational point is that the relevant advocacy happens outside the room — in communications with the prosecutor before an indictment is sought.