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Clark v. Arizona Convicted murderer (P) v. State (D)

Citation. 548 U.S. 735 (2006)
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Brief Fact Summary.

When Clark, who was without dispute a paranoid schizophrenic, was not allowed to present evidence of diminished capacity in his trial for first-degree murder, he pleaded violation of his right to due process of law.

Synopsis of Rule of Law.

A state does not violate due process of law by preventing the introduction of evidence showing diminished capacity by a criminal defendant.


During a traffic stop, Clark (D) shot and killed a police officer, and was prosecuted for first-degree murder. Clark admitted the shooting but brought his paranoid schizophrenia at the time of the incident as a defense, to prove that he did not have the specific intent to shoot an officer of the law or the knowledge that he was committing this specific crime. The trial court ruled that Clark could not use evidence showing that he was insane to rebut the presence of the mensrea. Thus psychiatric evidence could not be admitted to prove the absence of specific intent or of mensrea. Clark was convicted and the intermediate appellate court. The U.S. Supreme Court granted review.


Does a state violate due process of law by preventing the introduction of evidence showing diminished capacity by a criminal defendant?


(Souter, J.) No. A state’s prohibition of the introduction of diminished mental capacity by the defendant in a criminal case does not violate due process. The state prohibition applies only to evidence regarding mental capacity and mental disease, usually based on expert testimony,  rather than observation. Such a restriction, provided it has a good reason, is not a violation of constitutional rights, as the benefits outweigh the loss of the evidential value. Another point is that the consideration of such evidence is limited if the evidence is disallowed as a whole. Evidence regarding mental disease and mental capacity presents risks which can be limited by allowing only the insanity issue to be considered, upon which the burden of evidence rests on the defendant. Some of these risks are the debatable nature of some diagnoses of mental disease, the danger of the evidence being misleading and the risk of ascribing a greater level of certainty to the evidence of mental capacity than the experts intended to communicate. Firstly, the diagnosis does not reveal the uncertainty about what actually defines mental illness, which is not always agreed upon by mental health experts; secondly, the evidence of mental disease may lead jurors to mistakenly suppose that the defendant lacks reasoning, thought, willpower or moral discrimination because of his mental illness, when such may not be the case at all, even if the diagnosis is broadly correct, and the defendant is undisputed to belong to such a category; and finally, the expert opinions carry undeserved weight  when they supplement the diagnosis of mental capacity with their judgment of the defendant’s mental capacity, as to his inability to understand right or wrong, or to think through an action in the manner necessary to establish the mensrea. The danger is always present that in this type of evidence, unlike observational evidence, the expert will not be able to define the exact state of mental thought or capacity at the moment of the offense despite the most careful examination. The legal categories that are responsible for the definitions governing mental capacity judgments are not identical with psychological categories that define the psychiatrist’s judgments. These practical and theoretical problems pose a substantial risk that the expert testimony regarding mental capacity evidence will have an apparent but unintended and unreal authority. This risk and the inherent difficulty of evaluating the importance of evidence regarding mental disease are the basis of Arizona state’s decision to limit expert psychological or psychiatric evidence to consideration on the insanity issue, on which the defendant, as the party which stands to benefit, has the burden of persuading the court. The verdict is affirmed.


(Kennedy, J.) Clark should be allowed to introduce evidence of his lack of awareness or intent to commit the specific crime he is charged with, provided it is reliable and thought-through, so that he can prove he cannot be convicted of either knowingly or voluntarily killing a police officer. The evidence would help him to explain his conduct in a way which would help the facts to be cleared as to whether he was aware of his conduct in killing a police officer. It would help to explain the way he thought, the way he understood what he experienced and how his mental disease affected this process of understanding. There is no logic in strictly enforcing a separation of the observational evidence from the scientific explanation which makes it understandable. The element at issue here is the mensrea, which is based on the determination of facts. The fact of mental illness as established by expert testimony bears upon how he understood the world around him, or what he understood to be the facts at the time of the shooting. The court’s exclusion of this category of evidence is not convincing. Firstly, all mental illness evidence is not unreliable and so should not be excluded per se. Secondly, the fact that this is a complex question doesn’t change the justification for supplying the facts regarding a person’s mental illness to the jury if it could provide a crucial support for the defense. The confusion of the jury would be likely to be due to the mixing up of the defense based on insanity and the issue of intent, rather than due to expert evidence. The third point is that evidence regarding mental illness can be misleading at times, but in this case it is important to know whether Clark had mental illness since that bears directly on the question of the guilty mind. The expert testimony was meant to support the evidence given by lay witnesses. It would throw light on whether the defendant actually knew at the time that he was killing a human being, if not a police officer. The different interpretations placed by the state and defense experts on the effect of his mental illness on his mental state meant only that the evidence was debated, not undependable, misleading or irrelevant. The final placing of the burden of proof on the defendant as to his intent or knowledge of the crime he was committing is unconstitutional as the state has the responsibility of proving these elements of the crime beyond reasonable doubt.




In this case, the Court made the point that while not every state will find it necessary to exclude mental capacity or mental disease evidence, it is still a sensible choice by Arizona as the reasons given for channeling the evidence are to limit the risks while still preserving due process of law for the accused person.

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