## Facts

- In 1995, Kansas revised its insanity-defense statute to permit a defendant to introduce evidence of mental illness only to show he lacked the culpable mental state (mens rea) required for the charged offense; mental disease or defect was “not otherwise a defense” to criminal liability.
- Under the Kansas scheme, a defendant could use mental-illness evidence at the guilt phase to show a lack of cognitive capacity about the nature and quality of his acts (i.e., he did not know what he was doing), but could not obtain an acquittal based solely on moral incapacity (i.e., inability to distinguish right from wrong).
- Kansas law also allowed a defendant to present evidence at sentencing that mental illness impaired his ability to understand the moral wrongness or criminality of his conduct as a mitigating factor.
- In 2009, Karen Kahler filed for divorce from James Kahler, and she moved out of their home with their three children; Kahler became distraught.
- Months later, Kahler went to the home of Karen’s grandmother, where Karen and the children were staying, entered the home, and shot Karen twice.
- Kahler allowed his son to flee, then shot and killed Karen’s grandmother and his two daughters; all four victims died.
- The next day, Kahler turned himself in to police and was charged with capital murder.
- Before trial, Kahler moved to challenge Kansas’s insanity framework, arguing that the Fourteenth Amendment Due Process Clause required an insanity defense that would excuse a defendant who, because of mental illness, could not distinguish right from wrong.
- The trial court denied the motion, and a jury convicted Kahler of capital murder.
- During the penalty phase, Kahler presented evidence of his mental illness as mitigation, but the jury still imposed the death penalty.
- The Kansas Supreme Court affirmed the conviction and sentence, rejecting Kahler’s due process challenge to Kansas’s approach to insanity.

## Issues

1. Whether the Due Process Clause of the Fourteenth Amendment requires a State to provide an insanity defense that acquits a defendant who, because of mental illness, could not distinguish right from wrong.

## Decision

- The Supreme Court affirmed the Kansas Supreme Court.
- Due process does not require States to adopt an insanity defense that turns on “moral incapacity,” meaning an inability to recognize that one’s conduct is wrong.
- Kansas may limit mental-illness evidence at the guilt stage to negating mens rea and allow evidence of moral incapacity to be considered at sentencing as mitigation.
- Because the content of insanity defenses has differed across jurisdictions and time, no single “right-and-wrong” formulation is a fundamental requirement imposed on the States by due process.

## Legal Principles

- A state rule governing criminal responsibility violates substantive due process only if it offends a principle of justice “so rooted in the traditions and conscience of our people as to be ranked as fundamental.”
- The insanity defense has taken multiple forms in Anglo-American law, and States have long used different tests and different ways of treating mental-illness evidence in criminal cases.
- The Constitution does not mandate any one model of insanity, including a stand-alone defense based on inability to distinguish right from wrong.
- A State may structure its criminal law so that mental-illness evidence is relevant to criminal liability by negating the mens rea element of an offense, while handling other mental-illness considerations at sentencing.
- States retain broad authority to define the elements of crimes and the availability and contours of defenses, so long as their rules do not violate a fundamental due process limitation.

## Conclusion

Kahler v. Kansas held that the Fourteenth Amendment does not require States to recognize a traditional right-wrong insanity defense, and Kansas’s decision to confine mental-illness evidence at the guilt phase to mens rea (while permitting mitigation evidence at sentencing) is consistent with due process.


Kahler v. Kansas, 140 S. Ct. 1021 (2020)