The Supreme Court is stepping into the case of a convicted murderer who claims authorities concealed evidence that might have spared him a death sentence.

The justices have twice before reinstated the death sentence for Gary Bradford Cone, who was convicted of beating an elderly couple to death in Memphis during a robbery.

Cone acknowledged that he killed the couple, but said he was temporarily insane because of drugs and the stress of his wartime Vietnam experiences.

He argued that state and federal courts never considered his claims that the state withheld evidence of his drug use. A panel of the Cincinnati-based 6th U.S. Circuit Court of Appeals ruled 2-1 that Cone's plea had no merit. The dissenting judge said Cone's claims were never fairly considered by either state or federal courts.

The appeals court had twice before issued rulings favorable to Cone, but was overruled each time by the Supreme Court.