Clark v. Arizona

548 U.S. 735 (2006)

Quick Summary

Eric Michael Clark (defendant) fatally shot a police officer and was charged with first-degree murder. Clark asserted that his paranoid schizophrenia prevented him from forming the intent to kill. The trial court convicted Clark based on Arizona’s legal standards for insanity and mens rea.

The U.S. Supreme Court examined whether these standards violated Due Process. The Court concluded that states have discretion in defining legal insanity and affirmed the conviction, as cognitive incapacity is included within Arizona’s moral incapacity standard, and expert testimony restrictions were applied correctly.

Facts of the Case

Eric Michael Clark (defendant) was involved in a fatal shooting of a police officer during a traffic stop. Clark, who was diagnosed with paranoid schizophrenia, was charged with first-degree murder. The charge specified that Clark ‘intentionally and knowingly’ killed the officer while on duty. After being found competent for trial, Clark waived his right to a jury, opting for a bench trial.

He admitted to the shooting but claimed his mental illness prevented him from forming the specific intent to kill a law enforcement officer or from knowing he was doing so. During the trial, evidence of Clark’s mental illness was presented solely to support an insanity defense, not to contest his mens rea directly.

The trial judge, adhering to the state’s legal standards, did not consider Clark’s mental illness as a direct factor in determining his mens rea and found him guilty based on the evidence provided by the prosecution and the standards for insanity in Arizona. Clark was sentenced to life imprisonment without the possibility of release for 25 years and subsequently appealed his conviction.

Procedural Posture and History

  1. Clark charged with first-degree murder and found incompetent to stand trial; committed to state hospital.
  2. Competence restored; Clark opted for bench trial.
  3. Trial court denied Clark’s motion for judgment of acquittal; found him guilty of first-degree murder.
  4. Arizona Court of Appeals affirmed conviction; Arizona Supreme Court denied review.
  5. U.S. Supreme Court granted certiorari.

I.R.A.C. Format


Whether Arizona violated Due Process by barring consideration of defense evidence of mental illness on the issue of mens rea and by using an insanity test solely based on the capacity to tell right from wrong.

Rule of Law

No violation of due process occurred when Arizona used its insanity test based solely on the capacity to tell right from wrong or when it restricted consideration of defense evidence of mental illness only to its bearing on a claim of insanity, thus excluding its direct significance on the issue of mens rea.

Reasoning and Analysis

The Supreme Court held that states have significant discretion in defining criminal offenses and defenses, including the insanity defense. The Court observed that there is no universally accepted standard for legal insanity, and thus, due process does not mandate any particular formulation.

It was determined that cognitive incapacity is implicitly included within moral incapacity in Arizona’s insanity test, meaning that evidence showing a defendant did not understand the nature of his actions could still demonstrate that he did not know his actions were wrong.

The Court also addressed the exclusion of certain types of expert testimony on mental illness from consideration on the mens rea element. It clarified that while Arizona’s rule in State v. Mott limited consideration of expert testimony on mental disease or incapacity to insanity defenses, other types of evidence such as observation evidence were still admissible to rebut claims of mens rea.


The Supreme Court affirmed the judgment of the Arizona courts, upholding Clark’s conviction and the standards used by Arizona regarding insanity defenses and the consideration of mental illness in relation to mens rea.

Key Takeaways

  1. States have broad discretion in defining criminal offenses and the parameters of an insanity defense.
  2. Due process does not require a specific formulation of legal insanity across jurisdictions.
  3. Cognitive incapacity is considered a subset of moral incapacity within Arizona’s definition of insanity.
  4. Evidence showing a defendant did not understand his actions can still be relevant under Arizona’s moral incapacity standard for insanity.
  5. Expert testimony on mental disease or incapacity can be restricted to considerations of an insanity defense without violating due process.

Relevant FAQs of this case

What are the implications of mental illness on establishing mens rea in criminal law?

The presence of mental illness can affect whether a defendant possessed the necessary mens rea, or mental state, to commit a criminal offense. Generally, if a mental illness impairs an individual’s ability to understand the nature and quality of their act, or prevents them from knowing that what they are doing is wrong, it can negate mens rea.

  • For example: A person with severe delusional disorder who commits theft may genuinely believe the property was their own, potentially lacking the requisite intent to steal.

How does the legal standard for insanity affect a defendant's criminal responsibility?

A legal standard for insanity determines if a defendant, due to mental disease or defect, is incapable of understanding their actions or distinguishing right from wrong at the time of the offense, which can lead to a verdict of not guilty by reason of insanity.

  • For example: If someone with profound psychosis kills in the belief that they are acting in self-defense against an imagined threat, they may meet the criteria for legal insanity.

In what ways can expert testimony be used in the context of an insanity defense?

Expert testimony is often critical in presenting evidence about a defendant’s mental state and can support claims that mental illness impacted the defendant’s capacity to appreciate the criminality of their conduct or to conform their conduct to the requirements of law.

  • For example: A forensic psychologist may testify that a defendant diagnosed with bipolar disorder was experiencing a manic episode during which he could not control his behavior, potentially supporting an insanity defense.


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