Most cases charged out of the prosecutors' office go to trial. Today, the Fifth Amendment requires grand jury indictments for all serious crimes in all states. The United States Constitution does not grant defendants the right to a preliminary hearing.
Preliminary hearings are adversary proceedings.
In federal courts, bind-over decisions may be based wholly on hearsay evidence. The functions of the preliminary hearing vary from jurisdiction to jurisdiction. The grand jury proceeding is a secret proceeding. The Supreme Court has fashioned remedies for irregular grand jury proceedings through its interpretation of the Sixth Amendment. The prohibition against double jeopardy attaches as soon as a suspect is arrested.