18 U.S. Code § 3332 - Powers and duties

It shall be the duty of each such grand jury impaneled within any judicial district to inquire into offenses against the criminal laws of the United States alleged to have been committed within that district. Such alleged offenses may be brought to the attention of the grand jury by the court or by any attorney appearing on behalf of the United States for the presentation of evidence. Any such attorney receiving information concerning such an alleged offense from any other person shall, if requested by such other person, inform the grand jury of such alleged offense, the identity of such other person, and such attorney’s action or recommendation.

Whenever the district court determines that the volume of business of the special grand jury exceeds the capacity of the grand jury to discharge its obligations, the district court may order an additional special grand jury for that district to be impaneled.