Hill's lawyers have contended he should not be put to death because he's mentally disabled, which the state disputes. But it was concerns about the method of execution that led a judge to stop Hill's execution just hours before it was to take place in Jackson, WGCL-TV, Atlanta, reported.
"We are relieved that the Superior Court of Fulton County has stayed the execution of Warren Hill, a man with mental retardation who has an undisputed IQ of 70," defense attorney Brian Kammer said in a statement.
"Today, the court found that more time is needed to explore Mr. Hill's complaint, which raises serious concerns about the extreme secrecy surrounding the execution process in Georgia, and the new Lethal Injection Secrecy Act, which took effect one day before Georgia issued a death warrant for Mr. Hill.
"At this time, there is far too much we do not know about how the state intends to proceed in this, the most extreme act a government can take against a citizen.
"Ultimately, we are hopeful that the United States Supreme Court will hear Mr. Hill's pending petition for writ of habeas corpus, and will have the opportunity to consider the important new evidence in this case, that there is unanimous consensus among all the doctors who have examined Mr. Hill, including three who previously testified for the state, that he is a person with mental retardation, and thus ineligible for the death penalty."
Hill, who has been on death row for 21 years, faces execution for the 1990 slaying of a fellow prison inmate. He was in prison for killing his girlfriend at the time.
In emergency papers filed Friday, his attorneys allege the Lethal Injection Secrecy Act violates Hill's constitutional rights by intentionally shielding from judicial review the means by which the drug to be used were manufactured and obtained.
Production of the drug, pentobarbital, ended in 2011 after European manufacturers embargoed its importation to the United States, citing its use in executions.
As Georgia's stock of pentobarbital ran out in March, state officials have resorted to secrecy, and possible unlawful means, in obtaining it, the magazine The Atlantic reported Monday.
Hill's lawyers argued, in their brief Friday, the lack of judicial review creates a "grave risk" their client will be subjected to "excruciating and unnecessary pain and suffering" during the execution, creating a violation of Hill's Eighth Amendment right against "cruel and unusual punishment."