Yesterday the Supreme Court, in an opinion by Justice Kagan, decided Kahler v. Kansas, 589 U.S. ___, No. 18-6135 (2020) in favor of Kansas. The question presented was whether the Due Process Clause requires a state to acquit a defendant who, because of mental illness, could not tell right from wrong when committing the offense.

In Kansas, the insanity defense only encompasses cognitive incapacity, that is, the state only requires acquittal by reason of insanity if a defendant’s mental illness prevents him from understanding the nature of his actions and he is unable to form the requisite mens rea for the crime. No other mental illness compels an acquittal. So, for example, if a defendant presents evidence at his murder trial that he “did not understand the function of a gun or the consequences of its use,” a jury crediting that testimony must acquit him. But evidence that the defendant “killed someone because of an insane delusion that God had ordained the sacrifice. . . can play no role in determining guilt.” The Petitioner argued that Kansas’ failure to offer an insanity defense for this latter type of mental illness—moral incapacity—violates Due Process.

A majority of the Supreme Court disagreed. After an extensive historical review of the insanity defense, the majority concluded that the petitioner was unable to establish that due process requires a specific insanity defense test nor that Kansas’ rule “‘offends some principle of justice so rooted in traditions and conscience of our people as to be ranked as fundamental.’” The Court found no consensus for a particular insanity test at common law and even after M’Naghten’s Case, conflicting medical views about mental illness continue to influence the scope of the defense. In light of these diverging views, states should be free to define and revise insanity defense tests “as new medical knowledge emerges and as legal and moral norms evolve.” The Court also found significant that Kansas still allows a defendant to offer any mental health evidence at sentencing and that this evidence can persuade a judge to commit a defendant to a mental health facility instead of imposing a term of imprisonment.

What does this mean for me??
As Justice Breyer recognized in his dissent, jurisdictions are now free to eliminate “the core” of the insanity defense—that due to a defendant’s mental illness, he lacked the capacity to be morally blameworthy for his actions. Further, the majority’s ruling creates an arbitrary disparity as to who can invoke the insanity defense: a defendant who kills a person believing that the person was a dog can claim insanity, while a defendant who kills a person believing a dog ordered him to do the killing, cannot.

Notably, while the majority held that Kansas’ rule did not violate due process, the Court left open the possibility that the rule could be later challenged under the Eighth Amendment.

SCOTUSblog page here: https://www.scotusblog.com/case-files/cases/kahler-v-kansas/