(CNN)The Georgia State Board of Pardons and Paroles voted to deny clemency in the case of convicted murderer Warren Lee Hill, the board said Tuesday, hours before Hill's scheduled 7 p.m. execution.
Despite pleas by human rights groups and legal representatives that have argued that Hill's intellectual disability should make him ineligible for the death penalty, Hill is set to die Tuesday evening by lethal injection at the prison in Jackson, Georgia.
The board said in a release that its members "thoroughly reviewed the parole case file on the inmate which includes the circumstances of the death penalty case, the inmate's criminal history, and a comprehensive history of the inmate's life" to reach their decision.
"The clemency board missed an opportunity to right a grave wrong," said Brian Kammer, Hill's attorney.
"It is now up to the U.S. Supreme Court to ensure that an unconstitutional execution of a man with lifelong intellectual disability is prevented."
Hill has an IQ of approximately 70 and the "emotional capacity of a young boy," Kammer said.
Federal law — stemming from a 2002 Virginia case that went to the U.S. Supreme Court — says executing intellectually disabled individuals violates the Eighth Amendment's ban on cruel and unusual punishment. But the ruling also allows states to define intellectual disability. In Georgia, that means attorneys for death row inmates have to prove mental impairment "beyond a reasonable doubt."
"This is the strictest standard in any jurisdiction in the nation," Kammer said.
Hill's execution would come two weeks after the state executed Andrew Brannan, a Vietnam War veteran suffering from post-traumatic stress disorder who killed Laurens County Deputy Kyle Dinkheller in 1998. Kammer also was Brannan's counsel.
Kammer, who has represented Hill for 20 years, said in any other state, Hill would be serving a life sentence. Hill was sentenced to death in 1990 for killing fellow prison inmate Joseph Handspike, beating him to death with a nail-studded board. At the time, Hill had been serving a life sentence for the 1985 shooting death of his girlfriend Myra Wright.
"We acknowledge that Mr. Hill should be held accountable for his actions and behavior," Torin Togut, president of the Arc of Georgia, said in a letter written on Hill's behalf. "However, it is our contention that Mr. Hill, who has an intellectual disability, should not be subject to capital punishment."
The Arc is a nonprofit organization that advocates for and serves people with intellectual and developmental disabilities.
Hill also has the support of the American Association on Intellectual and Developmental Disabilities, the Georgia NAACP, and former President Jimmy Carter and his wife, Rosalynn Carter.
The victim's family and former jurors have also expressed support for mercy in Hill's case, saying they weren't given the option of life without parole when sentencing him to death.
Kammer said seven doctors agree that his client is intellectually disabled — including three doctors for the state who initially evaluated Hill and said he didn't meet Georgia's standard. Kammer said those doctors have since signed an affidavit admitting they felt rushed during Hill's examination and now believe he does meet the standard for "intellectually disabled."
In previous clemency hearings, attorneys for the state have argued that Hill served in the Navy, held a job and managed his money before killing his girlfriend — signs that he didn't necessarily meet the legal standard to be considered intellectually disabled, even though he has a low IQ.
But Kammer said examples of Hill achieving "self-sufficiency" don't make a strong case for his execution.
Several of the letters supporting Hill's clemency cite last year's Supreme Court decision that struck down a Florida law that used "unscientific standards for determining intellectual disability" for death row inmates.
Attorneys tried to use the Hall v. Florida decision as grounds to spare the life of Georgia inmate Robert Wayne Holsey, who was sentenced to death for the murder of a local sheriff's deputy. Holsey, who also had an IQ of 70, was executed in December.
Hill declined to request a special last meal, the Department of Corrections said in a release. He will be offered the institutional meal tray, consisting of shepherd's pie, mashed potatoes, red beans, cabbage relish salad, cornbread, sugar cookies and fruit punch.