The highly polarized court sidestepped the controversial issue of the Constitutionality of executing the mentally ill. Rather, the decision barred Panetti's execution because he was not allowed to submit evidence of his psychiatric disorder at the state court level.
Panetti, who killed his estranged wife’s parents, was found competent to stand trial after two jury trials on that issue. He represented himself at his 1995 murder trial. He was floridly psychotic and delusional, rambling insanely and attempting to subpoena Jesus Christ, John F. Kennedy, and other dead people.
In the 1986 case of Ford vs. Wainwright, the Supreme Court held that executing a person who is severely mentally ill constitutes cruel and unusual punishment, banned by the Eighth Amendment. However, the "Ford standard" is vague as to the required severity of the mental condition, and people on all sides of the issue had been hoping for clarification from the high court.
The Court's opinion and a dissenting opinion are available online.
More background on the Ford standard and on Panetti's case is available on my blog entry of April 20, “Too Sick to Die?”
A 28-minute video, "Executing the Insane: The Case of Scott Panetti," is available at: http://blip.tv/file/282532.