The defendant was convicted of and sentenced to death for killing his wife, who had filed for divorce, his two teenage daughters, and his wife’s grandmother, with whom the victims were staying. Before trial, the defendant filed a motion arguing that Kansas’ law on insanity violated the Due Process Clause of the Fourteenth Amendment. Before statutory changes enacted in 1995, Kansas followed the M’Naghten test for insanity. Under that test, a defendant is not guilty by reason of insanity if either (1) he did not know the nature and quality of the act he was doing or (2) if he did know, he did not know his act was wrong. In 1995, Kansas legislatively abolished the M’Naghten insanity defense and adopted a mens rea defense. The pertinent statute provides that it is a defense to prosecution that the defendant, as a result of mental disease or defect, lacked the culpable mental state required as an element of the offense charged. The statute provides further that a mental disease or defect is not otherwise a defense. The Kansas courts rejected the defendant’s due process challenge. The U.S. Supreme Court affirmed.

The six-member majority began by observing that the M’Naghten insanity formulation consists of two tests: a cognitive incapacity test (the defendant did not know the nature and quality of his act); and a moral incapacity test (the defendant did not know his act was wrong). The Kansas’ mens rea defense, according to the Court, retains the cognitive incapacity test for insanity and jettisons the moral incapacity test. For a state rule on criminal liability to violate the Due Process Clause, it must offend “some principle of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental.” Slip Op. at 14. The Court held that the moral capacity test is not such a principle and that the Due Process Clause does not compel states to adopt an insanity defense that turns on a defendant’s ability to know his act was wrong. The Court also noted that Kansas law allows a defendant to present mental health evidence at sentencing and that a judge may replace a defendant’s prison term with commitment to a mental health facility.

The three dissenting justices argued that Kansas had eliminated the core of the insanity defense by disallowing the defense for a defendant, who by reason of mental illness, “lacked the mental capacity necessary for his conduct to be considered morally blameworthy.” Dissenting Op. at 1. The dissent gave two examples to illustrate its view.

In Prosecution One, the accused person has shot and killed another person. The evidence at trial proves that, as a result of severe mental illness, he thought the victim was a dog. Prosecution Two is similar but for one thing: The evidence at trial proves that, as a result of severe mental illness, the defendant thought that a dog ordered him to kill the victim. Under the insanity defense as traditionally understood, the government cannot convict either defendant. Id. at 1–2.

 Under Kansas’ law, the defendant in Prosecution One could defend against the charge by showing that his mental illness prevented him from forming the mens rea for murder (intentional killing of a human being). The defendant in Prosecution Two has no defense under Kansas law because he acted with the necessary level of intent. The dissent observed that mental illness typically does not deprive individuals of the ability to form intent; rather, it affects their motivations for acting. As a result, Kansas’ approach requires conviction of a broad swath of defendants who would be adjudged not guilty under any traditional formulation of the insanity defense. In the dissent’s view, this result “offends deeply entrenched and widely recognized moral principles underpinning our criminal laws.” Id. at 21. The dissent rejected the idea that consideration of mental capacity at sentencing satisfies due process, finding that an insane defendant should not be found guilty in the first place.