If you ask someone outside the legal realm what exactly a "federal grand jury" is, he or she will likely explain it's a jury for a "grand, federal" type of case. While this wouldn't technically be incorrect, it is far too imprecise. Given the deeply rooted prominence of the federal grand jury in the United States legal system (not to mention how often it appears in news headlines), it is important for the average citizen to understand the purpose and function of this legal structure.
The concept of a grand jury goes back as far as the Magna Carta, England's written constitution, in 1215. In fact, grand juries were so entrenched in the English common law that the Founding Fathers explicitly provided for grand juries in the Bill of Rights. The Fifth Amendment states that "no person shall be held to answer to a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury . . ."
Selected at random "from a fair cross section of the community," grand juries sit for terms of 18 months and meet regularly for sessions. These sessions are led by a federal prosecutor, an Assistant United States Attorney, who presents evidence to the jurors with respect to a particular case. After reviewing the evidence and having an opportunity to question the witnesses, the grand jury decides whether there is probable cause to move forward with a written indictment-that is, to bring charges.
These proceedings are kept especially secret. Only the grand jury, prosecutor, witnesses being examined, and court reporter may be in the room during a grand jury proceeding. Neither a judge nor a witness's attorney may be present (although the witness is allowed to leave the room to ask his or her attorney questions). Such an exclusive crowd gives rise to the more controversial element of the federal grand jury: there is no individual present to raise or consider objections to the prosecutor's tactics. Consequently, federal grand juries almost always return an indictment presented by the Government as a prosecutor can easily sway the grand jury.