Grand jury

A grand jury is a legal body which has the power to conduct official proceedings to investigate possible criminal conduct. They also decide whether criminal charges should be brought. A grand jury may subpoena evidence and may compel the sworn testimony of witnesses who appear before it. Grand juries are made up of from 16 to 23 people in the United States. They meet for a period of one month up to a year. However, jurors may only have to meet for a few days each month. The juries meet in private. The suspected person, called a suspect, is not usually present. About half the states in the US do not regularly use grand juries. A preliminary hearing may be used instead. The Fifth Amendment to the United States Constitution requires the use of grand juries by the federal legal system for all capital and "infamous crimes" (cases involving treason, certain felonies or gross moral turpitude).
History.
In 1166 an enactment of King Henry II of England, called the Assize of Clarendon, called for "the oath of *twelve men from every hundred and four men from every vill" to meet and decide who was guilty of robbery, theft or murder. It was the early ancestor of the jury system and of the grand jury. The United Kingdom abolished grand juries in 1933. Many of their former colonies including 
Canada, Australia and New Zealand have also stopped using them. The United States is one of the few remaining countries that uses the grand jury. 
Criticism.
Grand juries are called by a federal judge and are required to supervise them. But judges almost never interfere. The grand jury is led by a federal prosecutor. He cannot testify or be present while the jury deliberates. But most federal grand juries will return any indictment presented to it. This led to the famous saying "a prosecutor can get a grand jury to indict a ham sandwich." They can subpoena anything they want with very few restrictions. In United States v. R. Enterprises, Inc., 498 U.S. 292 (1991), the Supreme Court of the United States ruled "federal grand jury subpoenas are presumed to be reasonable and the burden of showing unreasonableness is on the recipient."
A grand jury, state or federal, has two functions. The first is to go over all evidence of criminal wrongdoing and to issue an indictment only if there is enough evidence. Their other purpose is to investigate and help the prosecutor gather evidence. Critics claim grand juries have failed to do both.