Grand juries function today essentially as they did when the famous British jurist William Blackstone described them in his influential Commentaries in 1769: they are charged with hearing only “evidence on behalf of the prosecution: for the finding of an indictment is only in the nature of an enquiry or accusation, which is afterwards to be tried and determined.”
True to its name, the “grand” jury is normally larger than the “petit” jury assembled for ordinary trials. Supreme Court Justice Joseph Story, writing his Commentaries on the Constitution in 1833, stated that “the grand jury may consist of any number, not less than twelve, nor more than twenty-three.” Our modern grand juries usually consist of 23 citizens. But in any case, it takes only a majority, or 12 votes, for a grand jury to deliver an indictment. By contrast, the unanimous voice of 12 jurors is typically required for conviction in a criminal trial.
The grand jury only hears from the prosecutor. Its proceedings are secret. The accused and his counsel for defense are not even present. In light of all this, and because a bare majority is sufficient for an indictment, it is not surprising that a grand jury usually decides in favor of the prosecutor. Indeed, former New York Court of Appeals Chief Judge Sol Wachtler is widely credited with coining the famous statement that a good prosecutor can convince a grand jury to indict a ham sandwich. While that may be a bit of an exaggeration, it is true that grand jury proceedings are so heavily weighted in favor of the prosecution that many suspects today choose to waive their right to a grand jury and proceed directly to the petit jury of an ordinary criminal trial.