The Grand Jury is involved with matters of a criminal nature such as possession and distribution of controlled substances, use or unlawful possession of firearms, immigration, wire and other financial fraud, child pornography, environmental crimes, and bank robbery.
The Grand Jury performs an important function under our constitution - "Panel of the People" which stems from English common law and traces to the Magna Carta in 1215. It is the Fifth Amendment to the United States Constitution that mandates that no person may be required to stand trial in federal court on a felony offense charge until an indictment is returned by a Grand Jury, unless that right is waived.
A Grand Jury, which normally consists of 16 to 23 members, has a more specialized function. The United States attorney, the prosecutor in federal criminal cases, presents evidence to the Grand Jury for them to consider in determining whether there is "probable cause" to believe that a crime has been committed by the individual to be charged. If the grand jury decides there is enough evidence, it will return an indictment against the defendant that is filed with the court. Grand Jury proceedings are not open for public observation.