JACKSON (AP) — An inmate convicted of killing a prison guard must be re-evaluated to determine whether he is too intellectually disabled for the death penalty, the Mississippi Supreme Court said Thursday.

In a 5-4 ruling , justices ordered a fresh evaluation of Willie Russell, originally sentenced to death for stabbing and killing prison guard Argentra Cotton in 1989 at the Mississippi State Penitentiary at Parchman. The case will go before a Sunflower County Circuit Court judge, who will again be asked to decide whether Russell should be executed or spared.

Russell originally went to Parchman on convictions of robbery, kidnapping and escape after abducting a guard from the University of Mississippi Medical Center in Jackson and leading police on a high-speed chase in 1987. He was convicted of killing Cotton, had his death penalty set aside, and then was sentenced to death a second time. He came within an hour of being put to death in 1997 before a federal appeals court stopped the execution.

The current proceedings center on a 2002 U.S. Supreme Court ruling that issued a broad ban on the death penalty for people with mental disabilities.

Sunflower County Circuit Judge Better Sanders set aside Russell’s death sentence in 2015. But the state Supreme Court found that Sanders should have agreed with the state’s position that it needed to administer additional tests before its experts could form an opinion.

Associate Justice James Maxwell wrote for the majority that “Russell was never evaluated on the specific criteria for intellectual disability,” set out by the U.S. Supreme Court.

Chief Justice William Waller Jr., dissenting on behalf of the four judges, said there had been enough testing and would have allowed Russell’s commutation to stand.

Two earlier intelligence tests showed Russell’s IQ was low enough that he shouldn’t be executed. Waller wrote there was no reason to administer a third test.

Waller’s dissent argued that a 2006 exam was only incomplete because of a need for outside information on Russell’s school and life history that the defense provided as part of the hearing before Sanders.