Warren Hill is a killer on death row. He has twice been convicted of murder in the state of Georgia. He has an IQ of 70. Few would dispute these facts.

But as the 53-year-old Hill languishes in a Jackson, Ga., prison, his intellectual disability is casting a new light on the state's toughest-in-the-nation execution law, and has provoked a legislative debate on whether it's time for a change.

Hill's IQ straddles the threshold for what Georgia calls "mental retardation."

A panel of seven state and independent psychologists agrees he is "mildly mentally retarded" and should be precluded from the lethal injection needle.

That might satisfy Texas or Florida to spare Hill's life, as those capital-punishment states rely on a "preponderance of the evidence" to decide who should be put to death.

But not Georgia.

Warren Lee Hill is shown in this undated Georgia Department of Corrections photograph. He is currently 53 years old. (Reuters)

The Empire State of the South stands alone in America with a death-penalty law that requires a defendant prove intellectual disability "beyond a reasonable doubt" to win clemency.

Hill's case, however, has persuaded Georgia's lawmakers to study whether their burden of proof for mentally disabled death-row inmates is too harsh.

"We're the outliers here on the standard," said Republican B.J. Pak, the vice-chairman of the out-of-session committee hearing at the Georgia State Capitol.

"And you never want to be the outlier on these kinds of things."

Three stays so far

Georgia's department of corrections has tried three times since July 2012 to give Hill a fatal dose of execution drugs, only to be stopped by 11th-hour stays of execution.

In at least one of those instances, Hill already had a sedative in his system before the lethal injection was halted.

Disability advocates, the Southern Centre for Human Rights and the family of former president Jimmy Carter have called for Hill to be granted a reprieve.

Warren Hill timeline 1990 Hill, serving time for a 1986 slaying, beats his cellmate, Lee Handspike, to death 1991 Hill is sentenced to death for Handspike's murder 2000 Three state experts testify Hill is not mentally disabled July 2012 Hill is granted his first stay of execution 2013 State experts from 2000 say they now think Hill is mentally disabled Feb. 2013 Hill is granted a 2nd stay of execution July 2013 Hill is granted a 3rd stay of execution Oct. 24, 2013 Georgia lawmakers meet to rethink death-penalty bill

Even the family of Joseph Handspike, the cellmate who taunted Hill in 1990 and was later beaten to death by the condemned inmate with a nail-studded board, has appealed for Hill to be removed from death row on humanitarian grounds.

Kathy Keeley, executive director of the Atlanta-based group All About Developmental Disabilities, said the goal now is to get legislators to draft and introduce a new bill in January without the "beyond a reasonable doubt" language.

"Our Supreme Court decided years ago that you should not — and cannot — execute somebody with an intellectual disability," Keeley said.

The problem with Georgia, she added, was that the 2002 Supreme Court ruling allowed each state to define intellectual disability themselves.

"We just want to go and lie with the other states," she said.

Enlisted in the navy

In a 2000 hearing, the prosecution pointed to the fact that Hill was able to hold a job, enlist in the navy and even had a girlfriend as proof of his intellectual capacity.

But upon review years later, state psychiatrists recanted their testimony, saying their initial assessment was rushed, misinformed and that they didn't understand at the time that even intellectually disabled people can carry on such activities as part of adaptive coping skills.

Hill's IQ would put him in the bottom two per cent of the population, experts say.

His lawyer, Brian Kammer, said his client has a passive understanding of how close he's already come to death.

"Warren knows he's been through the wringer on this for some amount of time, and he also understands it's extraordinary he's still alive," Kammer said from his office at the Georgia Resource Centre, a non-profit practice operating beneath a pizzeria in east Atlanta.

"These close brushes with executions have been very, very difficult for him."

Georgia set precedent

Kammer allows that psychiatric diagnoses are, by their nature, very complex, with experts making assessments on "a reasonable degree of scientific certainty," rather than making absolute conclusions.

Hill's lawyer Brian Kammer, speaking outside the Fulton County Courthouse in Georgia on July 19, 2013, just after winning the most recent stay of execution. (Brian Kammer)

IQ measurement is also an imprecise science, with possible standard deviations of plus or minus five points.

Warren Hill's case "illustrates that people whose condition is right on that cut-off point, they're most at risk for being wrongfully executed," he said.

"When you get to these close cases, you really want the system to err on the side of finding" intellectual disability.

There's an ironic wrinkle to this case as well, observes Richard Dieter, director of the Washington-based Death Penalty Information Centre.

Dieter pointed out that, until 1988, no U.S. state had ever passed a law prohibiting the execution of inmates found "guilty but mentally retarded." Georgia took the first step with its provision.

"It's an interesting thing that Georgia was the first state to pass such a law," Dieter said.

"That was back in the '80s, but now there's a much broader understanding of these things. A lot has happened since Georgia acted, but now they're stuck with this outdated standard of proof, and Warren Hill is at the cusp of all this, trying to stay alive."