A grand jury is convened to decide if there's enough evidence presented by the prosecutor to bring an indictment (charge) against the person. There usually isn't a judge present. The defendant is not present.
If a person wants to plead guilty, s/he can just tell their attorney or the prosecutor. They can then plead guilty in court in front of a judge. That way, no witnesses need to testify.
If a person wants to plead guilty, s/he can just tell their attorney or the prosecutor. They can then plead guilty in court in front of a judge. That way, no witnesses need to testify.