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 state 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).