A grand jury is composed of a group of individuals whose main purpose is to determine whether to issue an indictment against an individual. This process of determining whether or not to issue an indictment is commonly known as a grand jury investigation. During a grand jury investigation, the grand jury makes no decision or conclusion as to the guilt or innocence of an individual. It only determines whether there is probable cause, or enough evidence to suggest, that an individual may have committed a crime.
Grand juries are often selected from a similar pool of citizens as trial juries, also known as petit juries, although grand juries usually consist of more members and typically convene for a longer duration of time than trial juries. A grand jury investigation usually consists of the prosecuting attorney presenting evidence and questioning witnesses in an effort to make the case to the grand jury that an indictment should be issued. Members of the grand jury are also allowed to ask questions of the witnesses. One of the hallmarks of the grand jury process is secrecy; during questioning of the witnesses, the person being investigated and his attorney are generally not present. This is to ensure that witnesses feel free to provide honest and open testimony, without the fear of retribution.
Once all of the evidence has been presented and all the witnesses have been questioned, the investigation enters the deliberation process. During deliberations no one except for members of the grand jury may be present. Once deliberations have been completed, the members of the jury vote as to whether or not they believe that sufficient evidence exists to warrant an indictment. In most court systems that utilize the grand jury system, the decision of the members need not be unanimous, but a minimum number of votes are usually required to issue an indictment.
The origins of the grand jury are found in feudal England where the earliest grand juries consisted of knights that were called to investigate alleged crimes in their communities. Grand juries were specifically mentioned in the English Magna Carta of 1215. Over time the concept of the grand jury investigation evolved from trying to determine who may have committed a crime, to deciding if enough evidence existed to accuse someone of a crime. The grand jury was thus seen as a way to protect the rights of the accused from unwarranted prosecution from an overzealous prosecutor.
While the idea of the grand jury originated in England, a grand jury investigation is typically only used today in the United States. The use of a grand jury is specifically mentioned in the United States Constitution and is required in all cases where a person is under investigation for a Federal, or national, crime that is punishable by imprisonment for longer than one year. Although a grand jury investigation is required on the Federal level, only about half of the states in the United States use grand juries.