WASHINGTON (AP) — The Supreme Court has refused to consider whether a criminal defendant has a constitutional right to plead not guilty by reason of insanity.

The justices on Monday rejected an appeal from convicted killer John Joseph Delling of Idaho, one of four states that bar defendants from claiming that they were legally insane, or unable to appreciate that what they did was wrong. The other states are Kansas, Montana and Utah.

Delling pleaded guilty in the slayings of two college students during a trip across the West in 2007. Delling suffers from acute paranoid schizophrenia and says he was in the grip of severe delusions when he killed the two men and wounded a third.

He was sentenced to spend the rest of his life in prison without the possibility of parole. His lawyers say he would have received treatment and a more lenient sentence with an insanity plea.

Justices Stephen Breyer, Ruth Bader Ginsburg and Sonia Sotomayor were in the minority in saying they would have heard the case.

Attorneys with the Constitutional Accountability Center, which filed a friend-of-the-court brief supporting the notion that defendants have a constitutional right to plead not guilty by reason of insanity, said they were disappointed by the high court’s decision not to hear Delling’s case.

Courts dating from ancient Greece have held that the integrity of the criminal justice system requires an insanity defense, Constitutional Accountability Center attorney Elizabeth Wydra said in a prepared statement.

“The court should have taken Mr. Delling’s case to make sure that every state in the nation respects this long history of legal and moral tradition and provides constitutionally-mandated due process of law,” Wydra said.

During Delling’s trial, medical experts and his mother said he had lived with mental illness since childhood and that his adolescence and adulthood were punctuated by violence and bizarre delusions.

His attorney, Gus Cahill, said during the trial that Delling started displaying symptoms of schizophrenia at 16 and became entrenched in an elaborate delusion that a group of children in his neighborhood had begun stealing his energy. Psychiatric expert Dr. George Woods testified on behalf of the defense that Delling believed he would die if the energy thefts were allowed to continue and that the murders were necessary for him to save his own life.

But the trial judge, Deborah Bail, said Delling showed an enormous amount of premeditation in planning the cross-country trip and murders, and that he would have killed more people if he hadn’t been arrested, noting that he had four more names on a list of his planned victims.

Delling first attempted to kill former classmate Jacob Thompson in Tucson, Ariz. He approached Thompson in his truck, shooting him in the face, shoulder and arm. Thompson survived the attack.

Delling next flew to Boise, Idaho, where he rented a car and laid in wait for Bradley Morse. As Morse left his workplace, Delling shot and killed him and dumped his body in a nearby pond.

Then Delling traveled to Moscow, Idaho, where he went to see his childhood friend David Boss. When Boss opened his apartment door, Delling shot him point-blank.

Delling, Boss and Thompson were all former classmates at Timberline High School in Boise. Police say Delling met Morse, who attended high school in nearby Meridian, on a gambling website and used the Internet to track him down. Morse was a student at Boise State University when he died. Boss attended the University of Idaho.