Why does a federal grand jury hear evidence from the prosecution without the defense present?

A federal grand jury operates under the Fifth Amendment to the U.S. Constitution to determine whether there is probable cause to believe a crime has been committed. The proceedings are designed to be inquisitorial and secret rather than adversarial, which is why the defense is typically not present.12

The primary purpose of this structure is to serve as a check against potentially oppressive prosecution by allowing a group of laypersons to review evidence before a formal indictment is issued. Because the grand jury's function is to decide if a trial is warranted—not to determine guilt or innocence—the process is kept informal and confidential. Ordinarily, suspects do not have the right to present evidence, call witnesses, or have an attorney present during these proceedings. This secrecy and lack of defense participation are intended to protect the integrity of the investigation and the privacy of those involved until a formal charge is returned.1