Defending the insanity defense

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The Supreme Court refused this week to review the murder conviction of an Idaho man who was prevented by state law from offering an insanity defense. The court’s abdication of its responsibility encourages other states to dismantle a central principle of Anglo-American law: that a defendant should not be held criminally responsible when mental illness makes it impossible for him to tell right from wrong.

Contrary to what viewers of television courtroom dramas may believe, a plea of not guilty by reason of insanity is seldom asserted and usually unsuccessful. But there are cases — probably more than the judicial system recognizes — in which it is clear from medical evidence that a defendant is not responsible for his actions.

The principle that such people may not be held criminally responsible was articulated in the famous M’Naghten Rule announced by the British House of Lords in an 1843 murder case: A defendant is insane if at the time of the crime he either didn’t know that what he was doing was wrong or was unable to understand the nature and quality of his act. Half the states, including California, employ a form of M’Naghten. In all, 46 states employ some version of the insanity defense, though some also provide for the (logically self-contradictory) verdict of guilty but mentally ill.


One state that doesn’t offer an insanity defense is Idaho, where Joseph Delling was convicted of shooting two of his friends to death because he thought they were “trying to steal his powers.” Idaho still requires prosecutors to prove that a defendant had “the mental capacity to form the necessary intent,” but, as Justice Stephen G. Breyer pointed out in dissenting from the court’s refusal to hear Delling’s appeal, that is a narrow exception.

Idaho’s law, Breyer noted, would benefit a mentally ill man who thought the man he shot was a wolf, but it wouldn’t be of any help to an equally deranged man who knew his victim was human but believed he had been ordered to act by “a wolf, a supernatural figure.” Yet in both cases, “the defendant is unable, due to insanity, to appreciate the true quality of his act, and therefore unable to perceive that it is wrong.”

As the Constitutional Accountability Center noted in its friend-of-the-court brief in the Idaho case, “The insanity defense was already a deeply entrenched part of our criminal law by the time of the Reconstruction, when the 14th Amendment’s Due Process Clause was added to the Constitution.” The Supreme Court should have used the Idaho case to make it clear that due process requires that an insanity defense be available. Instead, only three justices — Breyer, Ruth Bader Ginsburg and Sonia Sotomayor — were willing even to hear arguments on the issue. That may not be an insane outcome, but it’s an unjust one.