The US Supreme Court ruled Monday that a state need not adopt an incapacity test that turns on a defendant’s ability to recognize that his crime was morally wrong in order to comply with the Fourteenth Amendment’s Due Process Clause.

The case, Kahler v. Kansas, involves a man (Kahler) who was convicted of capital murder for shooting and killing his ex-wife, his two teenage daughters and his ex-wife’s grandmother in 2009.

Kahler appealed his conviction, arguing that Kansas’ incapacity test violated Due Process.

Kansas law provides that the cognitive incapacity test be used when a defendant raises an insanity defense. This test consists of  determining whether the defendant was able to understand what he was doing when he committed the crime.

Kansas law does not look into whether the defendant knew that what he was doing was morally wrong. It only looks at whether the defendant understood what he was doing (shooting the victims in this case) to determine whether the defendant should be acquitted or to determine whether a lesser punishment is appropriate.

Kahler argued that Kansas’ chosen test essentially abolished the insanity defense by refusing to take into consideration whether a mentally-ill defendant knew that what he was doing was morally wrong, and is, therefore, a violation of Due Process.

The US Supreme Court ruled that Due process does not require a state to adopt a specific test of insanity. It held that a state could choose which insanity test to adopt, that Kansas’ cognitive incapacity test did not eliminate the insanity defense since it does take into account a defendant’s mental illness at trial and at sentencing, and that the test, therefore, does not violate Due Process.

However, Justices Stephen Breyer, Ruth Bader Ginsburg and Sonia Sotomayor dissented from the court’s decision, arguing that Kansas did in fact eliminate a core element of the insanity defense by refusing to take into account the fact that the defendant, because of his mental illness, lacked the mental capacity to understand that his actions were morally wrong, thus violating Due Process.