我的理解（也许有误），把案子带到grand jury也是检察官。

The United States is virtually the only common law jurisdiction in the world that continues to use the grand jury to screen criminal indictments.[1][2] Generally speaking, a grand jury may issue an indictment for a crime, also known as a "true bill," only if it finds, based upon the evidence that has been presented to it, that there is probable cause to believe that a crime has been committed by a criminal suspect.Unlike a petit jury, which resolves a particular civil or criminal case, a grand jury (typically having twenty-three or more members) serves as a group for a sustained period of time in all or many of the cases that come up in the jurisdiction, generally under the supervision of a federal U.S. attorney, a county district attorney, or a state attorney-general and hears evidence ex parte (i.e. without suspect or person of interest involvement in the proceedings).