The Handbook for Federal Grand Jurors provides information on how a federal grand jury works.
The federal grand jury’s function is to determine whether a person shall be tried for a serious federal crime alleged to have been committed within the district where it sits.
Matters may be brought to its attention in three ways: (1) by the United States Attorney or an Assistant United States Attorney; (2) by the court that impaneled it; and (3) from the personal knowledge of a member of the grand jury or from matters properly brought to a member’s personal attention. In all these cases, the grand jury must hear evidence before taking action.
Much of the grand jury’s time is spent hearing testimony by witnesses and examining documentary or other evidence in order to determine whether such evidence justifies an indictment. In the usual case, the United States Attorney or one of the Assistant United States Attorneys will present the evidence of alleged violations of the law to the grand jury. These attorneys also advise grand jurors as to what witnesses should be called and what documentary evidence should be produced for examination by the grand jury. The grand jury may ask that additional witnesses be called if it believes this necessary.
Witnesses are called to testify one after another. Ordinarily, the attorney for the government questions the witness first, followed next by the foreperson of the grand jury. Then, the other members of the grand jury may question the witness.
Because of the need for secrecy, the law forbids anyone other than authorized persons from being present in the grand jury room while evidence is being presented. This means that only the grand jury, the United States Attorney or the Assistant United States Attorney, the witness under examination, the court reporter, and the interpreter (if the foreperson determines one is required) may be present. If an indictment should ultimately be voted, the presence of unauthorized persons in the grand jury room could invalidate it.
Occasionally, prior to answering a question, a witness may ask to leave the grand jury room to consult with his or her attorney.
Additionally, a witness who is appearing before the grand jury may invoke the Fifth Amendment privilege against self-incrimination and refuse to answer a question. In such a situation, the grand jurors may bring the matter before the court in order to obtain a ruling as to whether or not the answer may be compelled. One manner in which an answer may be compelled is by granting the witness immunity from prosecution in exchange for the witness’ testimony.
Normally, neither the person under investigation nor any witness on the accused’s behalf will testify before the grand jury. It is the responsibility of the grand jury to weigh the evidence presented to it in order to determine whether this evidence, usually without any explanation being offered by the accused, persuades it that there is probable cause to believe that a crime has been committed and that the accused was the person who committed it.
Secrecy is important. It protects the grand jurors from being subjected to pressure by persons who may be subjects of investigations by the grand jury or associates of such persons. Secrecy also encourages witnesses before the grand jury to give full and truthful information as to the commission of a crime. It also prevents tampering with or intimidation of such witnesses before they testify at trial.
After it has received evidence against a person, the grand jury must decide whether the evidence presented justifies an indictment, or “true bill,” which is the formal criminal charge returned by the grand jury. The United States Attorney prepares the formal written indictments that the grand jury wishes to present. But neither the United States Attorney nor any Assistant United States Attorney may remain in the room while the grand jury deliberates and votes on an indictment.
Upon the indictment’s being filed in court, the person accused must either plead guilty or nolo contendere or stand trial.
If the evidence does not persuade the grand jury that there is probable cause to believe the person committed a crime, the grand jury will vote a “no bill,” or “not a true bill.” When this occurs, no trial is required.
Read Handbook for Federal Grand Jurors.
Also here is a 2005 feature on How Federal Grand Juries Work by NPR