The U.S. Supreme Court is preparing to consider how far states can go toward eliminating the insanity defense in criminal trials as it reviews the case of a Kansas man sentenced to die for killing four relatives.

The high court planned to hear arguments Monday in James Kraig Kahler’s case. He went to the home of his estranged wife’s grandmother about 20 miles (32 kilometers) south of Topeka the weekend after Thanksgiving 2009 and fatally shot the two women and his two teenage daughters.

Not even Kahler’s attorneys have disputed that he killed them. They’ve argued that he was in the grips of a depression so severe that he experienced an extreme emotional disturbance that disassociated him from reality.

In seeking a not guilty verdict due to his mental state, his defense at his 2011 trial faced what critics see as an impossible legal standard. His attorneys now argue that Kansas violated the U.S. Constitution by denying him the right to pursue an insanity defense.

The nation’s highest court previously has given states broad latitude in how they treat mental illness in criminal trials, allowing five states, including Kansas, to abolish the traditional insanity defense. Kahler’s appeal raises the question of whether doing so denies defendants their guaranteed right to due legal process.

“Maybe they will establish some ground rules,” said Jeffrey Jackson, a law professor at Washburn University in Topeka. “They’ve been vague about what the standard is, and maybe now they’re going to tell us.”

Until 1996, Kansas followed a rule first outlined in 1840s England, requiring defendants pursuing an insanity defense to show that they were so impaired by a mental illness or defect that they couldn’t understand that their conduct was criminal. Now Kansas permits defendants to only cite “mental disease or defect” as a partial defense, and they must prove they didn’t intend to commit the specific crime. Alaska, Idaho, Montana and Utah have similar laws.