What Is a Grand Jury and How Does It Work?

The first step towards criminal proceedings

Empty chairs in jury box
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A grand jury is a legal body comprised of laypeople that determines whether there is enough evidence to bring criminal charges to trial. During grand jury proceedings, a prosecutor presents an accusation and supporting evidence to the grand jury. The grand jury then decides whether or not the prosecutor can proceed with a criminal trial.

Why Cases Go to a Grand Jury

The concept of a grand jury originated in England and became enshrined in the U.S. legal system through the Fifth Amendment, which requires all potential federal cases to proceed through a grand jury.

Only about half of U.S. states recognize grand juries as a way to pursue state criminal charges. In states that use grand juries, a grand jury indictment is the primary way to start criminal proceedings. Their importance and usage vary between states.

States that don't use grand juries use preliminary hearings for felony cases. Instead of impaneling a grand jury, a prosecutor files a criminal complaint which lists the name of the defendant, facts of the case, and relevant charges. After the complaint is filed, a judge reviews it in a public preliminary hearing. During this hearing, lawyers are present and the judge decides whether or not to indict the defendant. In some states, a person who has been accused of a crime can request a preliminary hearing.

How Grand Juries Are Selected

Grand juries are made up of randomly-selected laypeople. The grand jury members are asked to appear in court for varying lengths of time: some grand jury sessions last for months, but only require jury members to sit in court for a few days each month.

Grand juries are generally composed of 6 to 12 people just like a trial jury, but when a federal grand jury is called, 16 to 23 people may be required to show up for jury duty.

What Grand Juries Do

When a grand jury is convened, the jury members evaluate the strength of the prosecutor's evidence to determine if there is probable cause to issue an indictment.

Probable cause means that there are enough objective facts to support the prosecutor's claim.

The grand jury has tools at their disposal to find out if there is probable cause. They can subpoena witnesses to testify in court. In a grand jury, witnesses are typically questioned by the prosecutor and cannot have counsel present during questioning.

If jury members think there is enough evidence, they vote to issue an indictment: a document that signals the start of criminal proceedings by listing the crimes the defendant is accused of and explaining the jurisdiction of the court. This act requires a majority vote, which is either two-thirds or three-fourths,  depending on the jurisdiction.

In many ways, the grand jury acts as a check on the power of a prosecutor. Grand jury proceedings may also benefit prosecutors by giving them a chance to see if their evidence will be convincing for a future trial jury. 

Unlike most other court proceedings, grand jury proceedings take place in secret, which serves a few purposes:

  • An accused person may present a flight risk if he or she knows a grand jury has been convened. By keeping the proceedings a secret, the court reduces this risk. 
  • Secrecy ensures that no one who eventually gets cleared of any crime suffers from premature and wrongful damage to their reputation.

    The names of grand jury members are also kept secret to prevent bias. While secrecy can be helpful for maintaining confidentiality, it also makes the grand jury process somewhat of a mystery to most members of the public and raises questions about transparency in the court.

    Grand Jury vs. Trial Jury

    Grand juries function differently from trial juries. Trial juries are presented with evidence from the defense and the prosecution. The accused person is present in court and has a legal right to a defense attorney. In a criminal case, the judge asks the trial jury to decide whether someone is innocent or guilty of a crime beyond a reasonable doubt, which is is the highest burden of proof in the American legal system.

    A grand jury, on the other hand, needs only to decide whether there is probable cause to put someone on trial—a much lower burden.

    The accused does not have the right to appear before the grand jury and contest evidence brought by the prosecutor. Lastly, a grand jury has no power to convict someone of a crime—they can only issue an indictment.


    • "Grand jury." Britannica Academic, Encyclopædia Britannica, 9 Apr. 2018. academic-eb-com.resources.library.brandeis.edu/levels/collegiate/article/grand-jury/37676. Accessed 21 Jun. 2018.
    • United States, Congress, “Handbook for Federal Grand Jurors.” Handbook for Federal Grand Jurors, Administrative Office of the U.S. Courts.
    • “How Courts Work.” American Bar Association, www.americanbar.org/groups/public_education/resources/law_related_education_network/how_courts_work/pretrial_appearances.html.
    Grand jury investigations are shrouded in secrecy; violating that secrecy is considered criminal contempt and can also be considered obstructing justice. Those who are bound to secrecy include everyone but the witnesses: prosecutors, grand jurors, court reporters, and clerical personnel. Identities of grand jurors are kept secret.

    In 1946, Supreme Court created created the Federal Rules of Criminal Procedure, which simplified common law and codified grand jury secrecy in Rule 6, subsections (d) and (e). The first provision limited who could be present in grand jury sessions; the second imposed a general rule of secrecy.

    Grand jury proceedings are secret because:
    • Anyone being investigated cannot interfer with witnesses or otherwise tamper with the investigation.
    • Secrecy decreases the likelihood someone who is about to be indicted will escape before indictment.
    • Reluctant witnesses can speak more freely when their remarks will not be made public nor reach the target of an investigation.
    • Secrecy protects anyone who might be implicated, but who is not indicted.
    Witnesses are not sworn to secrecy in Federal grand juries, which allows witnesses to refute rumors surrounding their appearance or testimony before a grand jury.

    Length of the Grand Jury
    A "regular" federal grand jury has a basic term of 18 months; a court can extend this term for another 6 months, bringing the total possible term to 24 months. A "special" federal grand juriy can be extend another 18 months, bringing the total possible term to 36 months. State grand jury terms vary widely, but from a month to 18 months, with a year being average.

    Oath of the Foreman
    The oath of the foreman is generally like this, reflecting its roots in history:
    • "You, as foreman of this inquest, for the body of the County of ____ , do swear, (or affirm) that you will diligently inquire, and true presentment make, of such articles, matters, and things as shall be given you in charge or otherwise come to your knowledge, touching the present service; the commonwealth's counsel, your fellows' and your own you shall keep secret; you shall present no one for envy, hatred or malice; neither shall you leave any one unpresented for fear, favor or affection, hope of reward or gain, but shall present all things truly as they come to your knowledge, according to the best of your understanding (so help you God.)"
      Returning An Indictment
      After the prosecutor presents evidence, jurors vote on the proposed charges (the indictment), which were drafted by the prosecutor. If a majority of the jury believes the evidence shows probable cause of a crime, the jury "returns" the indictment. This act initiates criminal proceedings.

      If a majority of the jury does not believe the evidence shows probable cause of a crime, that "no" vote is called "returning a bill of ignoramus" or "returning a no bill." No criminal proceedings follow this vote.

      However, this does not necessarily mean the end to an investigation. A person who is suspected of having committed a crime is not protected by the constitutional prohibition of " double jeopardy" in this instance, because the person has not yet been "put in jeopardy" (made to stand trial).