Most people think of a jury as twelve individuals who sit in judgment of defendants charged with a crime. While that is true, that kind of jury is called a Petit Jury. A Grand Jury, on the other hand, is a group of twenty-three citizens called together behind closed doors to investigate suspected criminal conduct. 

In Pennsylvania a Grand Jury, if called together by the Attorney General of the state, has multi-county jurisdiction --that is they can investigate criminal activity anywhere in the state of Pennsylvania. A Grand Jury called together by one of the sixty-seven district attorneys in the several counties of Pennsylvania has jurisdiction to investigate criminal activity in their particular county.

Unlike a Petit Jury, which decides whether a person on trial is guilty or not guilty of the crime charged, a Grand Jury's function is to determine whether evidence exists to file a criminal complaint charging an individual with a crime. After hearing all of the evidence, a Grand Jury decides whether there is enough evidence to charge criminal wrong-doing. The evidence is presented to the Grand Jury by a prosecutor, either an Attorney General or a District Attorney who calls witnesses before the Grand Jury, normally by subpoenaing them to appear, and questions those witnesses. All this is done behind closed doors and the investigation is supposed to be confidential. If after hearing evidence the Grand Jury votes to issue a "Presentment," which summarizes the evidence the Grand Jury has heard, and recommends that the prosecutors file specific charges against wrong-doers. The prosecutor is not required to follow the Grand Jury's recommendation that criminal charges be filed. In most cases however, the prosecutor does follow the Grand Jury recommendations and often uses the Grand Jury presentment as the basis of the criminal complaint.