In Kahler v. Kansas, No. 18-6135 (March 23, 2020), the U.S. Supreme Court cited Model Penal Code § 4.01 in holding that the Constitution’s Due Process Clause did not require States to provide an insanity defense that compelled “the acquittal of any defendant who, because of mental illness, could not tell right from wrong when committing his crime,” consistent with the moral-incapacity test from M’Naghten’s Case, 10 Cl. & Fin. 200, 8 Eng. Rep. 718 (H. L. 1843).
In Kahler, the defendant was charged with capital murder for killing his wife, who had recently filed for divorce and moved out of their home, his two daughters, and his wife’s grandmother. The trial court denied the defendant’s pretrial motion, in which he argued that Kansas’s treatment of insanity claims—which provided that it was “a defense to a prosecution under any statute that the defendant, as a result of a mental disease or defect, lacked the culpable mental state required” for a crime or was incapable of understanding the nature and quality of his or her actions, consistent with M’Naghten’s cognitive-incapacity test, but did not permit an insanity defense based on M’Naghten’s moral-incapacity test—‘“violate[d] the Fourteenth Amendment’s Due Process Clause’ . . . by allowing the conviction of a person ‘who [could not] tell the difference between right and wrong.”’ The jury found the defendant guilty and imposed the death penalty. The Kansas Supreme Court affirmed, holding that “due process [did] not mandate that a State adopt a particular insanity defense.”
After granting certiorari, the U.S. Supreme Court affirmed, holding that the Due Process Clause did not require States to adopt the two-prong approach, including the moral-incapacity test from M’Naghten and acquit a defendant who could not distinguish right from wrong when committing his crime. Associate Justice Elena Kagan, writing for the majority, explained that “[u]nder well-settled precedent, a state rule about criminal liability—laying out either the elements of or the defenses to a crime—violate[d] due process only if it ‘offend[ed] some principle of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental.’” The Court reasoned that there were a diverse range of States’ approaches to insanity defenses that did not follow the test that the defendant argued the Constitution required, pointing out that “many States follow[ed] the Model Penal Code [§ 4.01(2)] in prohibiting psychopaths from raising the defense,” and concluding that “[n]o insanity rule in this country’s heritage or history was ever so settled as to tie a State’s hands centuries later.”
Dissenting, Associate Justice Stephen G. Breyer argued that Kansas “eliminated the core of a defense that has existed for centuries: that the defendant, due to mental illness, lacked the mental capacity necessary for his conduct to be considered morally blameworthy.” Justice Breyer pointed out that, in “Kansas’ early years of statehood,” it had followed the M’Naghten two-prong test “as the cardinal rule of responsibility in criminal law” for more than a century before enacting legislation adopting a mens rea approach. He agreed with the majority that the M’Naghten test was not constitutionally required, but argued that it was “a prominent expression” of the fundamental principle that “mental illness [could] so impair a person’s mental capacities” as to render the person “not properly the subject of the criminal law.” Justice Breyer noted that the “overwhelming majority of U.S. jurisdictions recognize[d] insanity as an affirmative defense that excuses a defendant from criminal liability even where he was capable of forming the mens rea required for the offense,” and that “[t]hirteen States and the District of Columbia [had] adopted variants of the Model Penal Code test, which combine[d] volitional incapacity with an expanded version of moral incapacity.” He noted that some of those States “interpret[ed] knowledge of wrongfulness to refer to moral wrong, whereas others h[e]ld that it mean[t] legal wrong,” but he argued, citing the Explanatory Note to § 4.01, that there was no indication that those two interpretations made a meaningful difference in practice.
Read the full opinion here.