The insanity defense is based on evaluations by forensic mental health professionals with the appropriate test according to the jurisdiction. Their testimony guides the jury (or judge in a bench trial). But they may not testify to the defendant's criminal responsibility. This is for the jury or judge to decide. Mental health experts may testify as to whether at the time of the crime the defendant understood what he did was wrong. If the defendant were acting under a delusion at the time and could still determine right from wrong, he is not insane and may be punished. 