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Name: Clark v. Arizona
Case #: May-66
Court: US Supreme Court
District USSup
Opinion Date: 06/29/2006
Subsequent History: 126 S.Ct. 2709; 165 L.Ed.2d 842

Due process neither requires a state to use both prongs of the M’Naughten insanity test or prohibits it from restricting consideration of defense evidence of mental illness and incapacity to a claim of insanity. Defendant was tried for the murder of a police officer, and he sought to introduce evidence of mental illness to raise the affirmative defense of insanity, and to rebut the prosecutor’s evidence of mens rea. However, pursuant to state law, the trial court did not allow defendant to rely on the insanity evidence to dispute mens rea based on Arizona case law which does not permit evidence of mental disease short of insanity to negate mens rea. Moreover, Arizona law on insanity takes an abbreviated approach to M’Naughten because while it recognizes the moral incapacity prong, it does not recognize the cognitive capacity prong. Defendant argued both limitations violate due process. The high court affirmed and found Arizona’s approach comports with due process. Noting that the states had varied approaches with respect to legal insanity, the Court held due process “imposes no single canonical formulation of legal insanity.” Thus, a state may adopt an insanity test that focuses solely on moral incapacity. In fact, “cognitive incapacity itself is enough to demonstrate moral incapacity.” Additionally, Arizona’s prohibition of diminished capacity evidence does not violate due process because a defendant’s “right to introduce relevant evidence can be curtailed if there is a good reason for doing” so. Arizona has good reasons, which include: the controversial character of the evidence, its potential for misleading the jury, and the danger it will be accorded greater certainty than it deserves. As a result, there is no due process violation.