Upon the trial of the defense of insanity at the time of the offense, the members of the sanity commission may be called as witnesses by the court, the defense, or the district attorney. Regardless of who calls them as witnesses, the members of the commission are subject to cross-examination by the defense, by the district attorney, and by the court. Other evidence pertaining to the defense of insanity at the time of the offense may be introduced at the trial by the defense and by the district attorney.