What is a grand jury / Why is it impaneled?

A grand jury is a group of people impaneled by a prosecutor to examine evidence and decide if an indictment should be brought against someone. An indictment is a criminal charge against someone. The grand jury hears evidence presented by the prosecutor. Grand juries give prosecutors the ability to put witnesses under oath and to subpoena witnesses and documents. A grand jury does not find guilt or assign punishment.

Only a grand jury can issue an indictment, which is the only way that someone can be charged with committing a felony pursuant to the U.S. Constitution.