A convicted killer on death row in Tennessee since 1984 could be spared execution following arguments Tuesday at the Supreme Court.

The justices showed rare bursts of anger in discussing a local prosecutor's failure to turn over key evidence to lawyers defending Gary Bradford Cone.

The withheld information appears to bolster claims that Cone was in a drug-induced psychotic state when he beat to death an elderly couple during a robbery in Memphis.

"You're saying that the lawyer, the trained lawyer for the government, who knew this information and knew the defense, just what? Just overlooked it by accident? Just what?" Justice Stephen Breyer demanded of Jennifer Smith, representing Tennessee.

A few minutes later, Justice David Souter addressed Smith after she said prosecutors were not required to hand over the evidence in question. "I believe you have just made a statement to me that is utterly irrational," Souter said.

Cone does not deny killing Shipley Todd, 93, and his wife, Cleopatra, 79. But Cone put on an insanity defense at trial, arguing that he was a drug addict who suffered from post-traumatic stress syndrome following military service in Vietnam.

The prosecutor referred to Cone's defense as "baloney" and the jury sentenced Cone to death.

The evidence that was not provided to his lawyers included police and FBI communications identifying Cone as a drug user and as an addict, and witness statements describing his behavior as "weird" and "wild-eyed."

The Supreme Court has twice before reinstated Cone's death sentence, but on different grounds. His lawyer, Thomas Goldstein, argued Tuesday that Cone has never had a hearing that considered the concealed evidence and whether it justifies converting his sentence from death to life in prison.

In a second criminal case Tuesday, the court debated whether a police officer may frisk a passenger in a car that has been stopped for a traffic violation when there is nothing to indicate the passenger has committed a crime or is about to do so.

The justices appeared willing to accept Arizona's argument that traffic stops are inherently dangerous for police and that such pat-downs are permissible when an officer has a reasonable suspicion that the passenger may be armed and dangerous.

But the court seemed more skeptical of the Bush administration's argument in the case that the police may frisk anyone they encounter, whether in a car or on the street, without some indication of criminal behavior.

The cases are Cone v. Bell, 07-1114, and Arizona v. Johnson, 07-1122.