Convicted murderer James K. Kahler's attorneys pressed the U.S. Supreme Court on Monday to find unconstitutional a Kansas law forbidding a defendant from invoking a free-standing defense of not guilty by reason of insanity.

Kansas is among a handful of states that forbid defendants from avoiding conviction by asserting they didn't know what they were doing was morally wrong due to mental illness. The question before the court in Washington, D.C., was whether Kansas statute adopted in the 1990s violated due process rights and protections against cruel and unusual punishment.

"If the person has the capacity to know that what he did was a violation of the criminal law, and that's the defense that is provided by a state, is that unconstitutional?" Justice Samuel Alito asked Kahler's appellate counsel.

"No," said Sarah Schrup, arguing on Kahler's behalf. "For centuries, criminal culpability has hinged on the capacity for moral judgment, to discern and to choose between right and wrong. The insane lack that capacity."

Kahler was sentenced to death for the 2009 slaying with a high-powered rifle of four family members, including his estranged wife and two daughters, in Burlingame. Kahler allowed his son to escape the Osage County residence, but his wife's grandmother's Life Alert device captured audio inside the home that included Kahler saying, "I am going to kill her." The audio recorded a daughter's screams for help. The grandmother and one daughter identified Kahler as the shooter before dying.

The trial court declined to allow Kahler to raise an insanity defense centered on deep depression. The Kansas Supreme Court upheld his convictions and rejected his argument regarding the insanity defense.

Toby Crouse, solicitor general of Kansas, told the justices it would be less than fruitful for the Supreme Court to make use of the Kahler case to define a rigid rule of constitutional law on insanity. He said the nation's highest court had allowed state legislatures and Congress to determine whether a person should or shouldn't be held responsible for a crime.

Kansas' statute implemented in 1995 requires a person to be held criminally liable if the offense was done intentionally, knowingly or recklessly despite mental defects. In Kansas, mental status can be presented as a mitigating factor to a jury or judge at sentencing.

"What Kansas does is it identifies those with intent to commit a crime — punishes those," Crouse said.

Justice Sonia Sotomayor said she had a problem with Kansas' "mens rea" or intent test because it didn't excuse from prosecution men and women who for centuries would have been considered lunatics.

"Many of them know they're killing somebody. So, intent under your mens rea test is met. They absolutely know they're killing someone; they just have no ability to say no," Sotomayor said.

Elizabeth Prelogar, assistant to the solicitor general in the U.S. Department of Justice, argued on Kansas' behalf by noting the Supreme Court long ago granted states principal responsibility for balancing medical, moral and legal judgments woven into insanity rules.

"I think for this court to try to articulate a theory of moral culpability could throw into question state laws across the nation that are trying to make these difficult judgments," she said.

Justice Elena Kagan echoed other members of the court while pointing to evidence Kahler was a person of intelligence who concealed his presence outside the house until storming inside to gun down four family members. Kahler elected not to shoot neighbors who assumed he was a burglar, eluded police by driving with his lights off and turned himself in the next day without incident.

"I mean, honestly, you can't say this, but I can," Kagan told Kahler's attorney. "In none of these 46 states, I'm guessing, would your client be found insane."

Schrup said the insanity defense was raised in less than 1% of cases nationally and was successful in one-fourth of them. Kansas stands as an outlier in regards to the insanity defense because nearly every other state and the military and federal court systems allow the accused, if diagnosed with a mental disease, to raise the insanity defense with respect to being prosecuted for a crime.

Chief Justice John Roberts piled on by pointing to evidence at trial indicating Kahler thrived on self-importance, was controlling and a tightwad.

"Maybe that's not the best way to order your life, but if that's what you mean by insanity, you can understand why that might cause some reservations," Roberts said.

Schrup said Kahler should have been granted the right under Kansas law to mount an insanity defense for consideration by the jury. The evidence would have revealed more forcefully Kahler's compromised mental state, she said.

She said Kahler's appeal wasn't about a person's well-reasoned ethical standards nor a justification of a violent act. The issue is whether Kansas should recognize the inability of a person to tap into the part of the brain that assesses right versus wrong, she said.

Kahler was a Kansas State University engineering graduate who earned a master's degree in business administration in Colorado. He met his wife, Karen, in Manhattan and they had three children — Emily, Lauren and Sean. Karen Kahler had an affair with a Texas woman. Kahler was arrested for assaulting his wife after the family moved to Columbia, Mo. Karen Kahler filed for divorce in early 2009.

In Burlingame on Nov. 28, Kahler drove to the home of Dorothy Wight, his wife's grandmother. He burst into the residence and shot his wife twice. He fatally wounded Wight, Emily, 18, and Lauren, 16. He fired seven shots, and six were considered lethal by investigators.