WASHINGTON - The Supreme Court has let stand the murder conviction of a paranoid and delusional Idaho man who was denied the opportunity to mount an insanity defense.

Three justices dissented, arguing that the court should incorporate the long-standing insanity defense into the Constitution.

Soon after John Hinckley Jr. was acquitted of the attempted assassination of President Ronald Reagan by reason of insanity in 1982, Idaho and three other states abolished the insanity defense from their criminal laws. The others were Kansas, Utah and Montana.

Joseph Delling was a "paranoid schizophrenic" who shot and killed two of his friends because he believed they were "trying to steal his powers," according to Idaho prosecutors.

Delling, then 21, had become "a type of Jesus," he later explained, and the men he killed were his childhood friend David Boss and Brad Morse, whom he had met playing online video games.

Delling had carefully planned the killings, and prosecutors successfully argued he had the intent to commit murder, even if he did not understand why it was wrong. Idaho law says "mental condition shall not be a defense to any charge of criminal conduct."

Delling was sentenced to life in prison for the killings, and the state Supreme Court upheld his conviction and sentence last year.

Stanford law Prof. Jeffrey Fisher appealed Delling's case back to the Supreme Court, contending that an insanity defense is required under the Constitution, either as an aspect of "due process of law" or through the ban on "cruel and unusual punishment."

Punishment is traditionally justified on the basis of an individual consciously choosing evil over good, Fisher wrote. "Laws such as Idaho's abandon that basic tenet," he said.

But the court turned down Delling's petition Monday, over dissents by Justices Stephen G. Breyer, Ruth Bader Ginsburg and Sonia Sotomayor. It takes the votes of four justices to hear an appeal.

Breyer said Idaho law "permits the conviction of an individual who knew what he was doing, but had no capacity to understand that it was wrong." That could allow the murder conviction of a defendant who "due to insanity, believes that a wolf, a supernatural figure, has ordered him to kill the victim," he said.

While the Supreme Court has approved states that limited the use of the insanity plea, it has never taken up the question of whether there is a constitutional right to the defense. All states and the federal government once allowed the insanity defense. But that changed with the public outrage over Hinckley's acquittal.

The Washington Post contributed to this report.