There is universal agreement in the United States that an individual convicted of a capital crime who is mentally incompetent may not be executed. To do so would violate the Constitution's ban on cruel and unusual punishments.
But just how mentally ill does a defendant have to be to trigger that broadly accepted Eighth Amendment prohibition?
That is the question the US Supreme Court takes up on Wednesday in a case involving the often bizarre legal odyssey of Texas death row inmate Scott Panetti.
Mr. Panetti, who has a long history of mental illness, was found guilty of the 1992 double slaying of his wife's parents. He shot them at close range in their kitchen as his wife and his three-year-old daughter watched. He took the child and his wife hostage, but later surrendered and confessed to police.
After being found competent to stand trial, Panetti fired his lawyer and represented himself. For the trial, he donned a Tom Mix-style cowboy outfit complete with boots, bandana, and hat.
He argued an insanity defense, advising the jury that only an insane person could prove insanity. Then he tried to subpoena 200 witnesses to testify on his behalf, including John F. Kennedy, the Pope, and Jesus. As one psychiatrist put it: Mr. Panetti's mind "saddles up and rides off in all directions."
Panetti testified at his own trial. He assumed an alternate personality named "Sarge," who recounted in a barely coherent babble impressionistic details of the killings.
The jury found him guilty, and the next day sentenced him to death.
Panetti, who refuses to take any medication, has become a jailhouse preacher, perpetually studying and quoting his well-worn Bible. His lawyer says he is convinced that his religious devotion is the true reason for his death sentence.
"Mr. Panetti believes that demonic forces, in league with the State of Texas, have orchestrated his execution in a final effort to prevent him from preaching the gospels of Jesus Christ," writes Panetti's lawyer, Keith Hampton of Austin, in his brief to the court. "According to Mr. Panetti, the State of Texas is using the murder of his wife's parents as a pretext to fulfill the devil's plot to silence him."
This is the core of the issue before the Supreme Court: Whether a death row inmate whose delusions prevent him from understanding the connection between his crimes and his imminent execution is mentally competent enough to face the death penalty.
Every judge or jury in Texas that has considered his case has concluded that Panetti has a mental illness but that he is nonetheless mentally competent enough to be executed.
The test in Texas is whether Panetti is aware that he is to be executed and aware of the state's reason for meting out that punishment.
Panetti's lawyer argues that the Texas standard is too low. Rather than mere awareness, the condemned man must be capable of having a rational understanding of the connection between his crime and his punishment, Mr. Hampton says.
"There is a big difference between knowing you are in a room and knowing why you are in a room," says Richard Dieter of the Death Penalty Information Center in Washington.
If Panetti doesn't understand why he is being executed, it undermines one of society's key goals behind the punishment – retribution, Panetti's lawyer says.
Others disagree. "Retribution is not focused on the mind of the offender," says Kent Scheidegger of the Criminal Justice Legal Foundation, in a friend of the court brief. "The focus of retribution is on society as a whole and what makes for a just society."
A just society punishes those who are morally responsible for their crimes, he says. "Panetti knows what he did and knows that he has been sentenced to death for the crime," Mr. Scheidegger writes. "His delusional belief in a conspiracy against him does not negate his moral responsibility for the crime he chose to commit and still knows he committed."
Panetti's lawyer counters that retribution is designed to force the offender to endure suffering proportionate to his crime to pay a debt owed to society. That is why the offender's mental capacity at the time of punishment is crucial to retribution, Hampton says. "The offender must suffer for the right reason before the community can confidently conclude that he is getting his just desserts for his wrongdoing," Hampton writes.