"The United States is the only common law jurisdiction in the world that continues to use the grand jury to screen criminal indictments. Generally speaking, a grand jury may issue an indictment for a crime, also known as a "true bill", only if it finds based upon the evidence that has been presented to it that there is probable cause to believe that a crime has been committed by a criminal suspect. Unlike a petit jury, which resolves a particular civil or criminal cases, a grand jury (typically having twenty-three or more members) serves as a group for a sustained period of time in all or many of the cases that come up in the jurisdiction, generally under the supervision of a federal U.S. attorney, a county district attorney, or a state attorney-general and hears evidence ex parte (i.e. without suspect or person of interest involvement in the proceedings)."..............
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New York [edit]
In New York State, while a person can initially be charged with a felony via a sworn written accusation alone (a "felony complaint"),[24] the state constitution provides a defendant with a right to have all felonies prosecuted by way of a grand jury indictment.[25] This right can be waived by a defendant, who can then be prosecuted using an indictment substitute called a "superior court information."[26] Grand juries are composed of between 16 and 23 jurors (16 being a quorum for all proceedings) and indictments require a minimum vote of 12 such jurors.[27] Grand juries may produce not only indictments but may direct the filing of misdemeanor charges in local courts, the removal of cases to Family Court, and may also issue “grand jury reports” concerning malfeasance of public officials and recommending their discipline.[28]
Both the prosecutor and the grand jury itself have the right to call witnesses to testify before the grand jury.[29] With few exceptions, every witness who testifies before a grand jury receives transactional immunity automatically, whether they invoke their right to silence or not.[30] If a grand jury is considering criminal charges against a person, that person has a right to testify before that grand jury, provided they make a timely written demand and then agree to waive their right to immunity.[31] Despite this fact, an unwitting target of a grand jury proceeding has no right to be informed that their case is even being considered by a grand jury in the first place, unless they have already been arraigned on a felony complaint charging a related crime and are awaiting a preliminary hearing on that complaint.[32]"
http://en.wikipedia.org/wiki/Grand_juries_in_the_United_States#New_York
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