It would be more nearly correct to say that the judge does not have the authority to accept or reject a plea of not guilty by reason of insanity. That is a defense, and as such is a matter to be determined by the trier of fact, namely the jury....
It would be more nearly correct to say that the judge does not have the authority to accept or reject a plea of not guilty by reason of insanity. That is a defense, and as such is a matter to be determined by the trier of fact, namely the jury. The sole--and unusual--exception would be if the defendant opted for a bench trial by the judge himself. In that event, the Judge would, as the trier of fact, decide if the defendant was, in fact, not guilty by reason of insanity.
The above answer states that in many states, the defendant must prove that he or she is insane. This is not true. In fact, in EVERY state an insanity defense is an affirmative defense that the defendant must prove by clear and convincing evidence. The prosecution has no burden in ANY state to prove a defendant is sane; it must only argue that the defendant has not met the burden of proof of an insanity defense, and of course prove that the defendant is guilty of the crime beyond a reasonable doubt. Please note that the burden of proof for the prosecution is greater than that for the defendant; still, as an affirmative defense, the burden of proof of an insanity defense falls on the defendant, not the prosecution.
The only rules that differ from state to state are the definitions of insanity. In my state, the common law M'Naughten Rule is still in effect; which states that at the time of the offence, the defendant was incapable of distinguishing between legal and moral right and legal and moral wrong. Other states have other definitions, but in every state, it is necessary for the defendant to prove that, but for his mental incapacity, the crime would never have been committed. The fact that one suffers from a mental defect is not in and of itself sufficient to absolve one of responsibility.