The 11th U.S. Circuit Court of Appeals granted its stay of execution as 52-year-old Warren Lee Hill was being prepared for lethal injection. In a 2-1 decision, a panel of the appeals court said further review is needed of recent affidavits by doctors who changed their minds about Hill's mental capacity.

"In other words, all of the experts -- both the State's and the petitioner's -- now appear to be in agreement that Hill is in fact mentally retarded," judges in the majority wrote in their order.

The state court of appeals also issued a stay to allow more time to consider a challenge related to the state's lethal injection procedure.

Earlier in the day, the state parole board, the Supreme Court of Georgia and the U.S. Supreme Court had all declined to stop the execution.

"We are greatly relieved that the Eleventh Circuit Court of Appeals has stayed the execution of Warren Hill, a person with mental retardation. All the doctors who have examined Mr. Hill are unanimous in their diagnosis of mental retardation," defense attorney Brian Kammer said in an email.

A spokeswoman for the state attorney general declined comment.

Hill was sentenced to die for the 1990 beating death of fellow inmate Joseph Handspike. Authorities say he used a board studded with nails to bludgeon Handspike while he slept and other prisoners pleaded with Hill to stop. At the time Hill was already serving a life sentence for murder in the 1986 slaying of his girlfriend, Myra Wright, who had been shot 11 times.

Hill has received support from various activists and from former President Jimmy Carter and his wife Rosalynn.

"Georgia should not violate its own prohibition against executing individuals with serious diminished capacity," President Carter said in a statement.

Hill was originally set to be executed in July, but the state delayed his execution when it changed its execution procedure from a three-drug combination to a one-drug method. The state Supreme Court then further delayed the execution after Hill's lawyers filed a challenge saying corrections officials violated administrative procedure when they made the change. The state's high court earlier this month denied that challenge, and Hill's execution was reset for Tuesday.

Hill's lawyers argue that he is mentally disabled and therefore shouldn't be executed. The state maintains that the defense failed to meet its burden of proving beyond a reasonable doubt that Hill is mentally disabled.

Death penalty defendants in Georgia have to prove they are mentally disabled beyond a reasonable doubt to avoid execution, the strictest standard in the country. Hill's lawyers have said the high standard for proving mental disability is problematic because psychiatric diagnoses are subject to a degree of uncertainty that is virtually impossible to overcome. But Georgia's strict standard has repeatedly been upheld by state and federal courts.

Georgia passed a law in 1988 prohibiting the execution of mentally disabled death row inmates, and the U.S. Supreme Court ruled in 2002 that the execution of mentally disabled offenders is unconstitutional.

Hill's lawyers last week released new sworn statements from the three doctors who examined Hill in 2000 and testified before the court that he was not mentally disabled. The doctors wrote in their new statements that they were rushed in their evaluation at the time, they have acquired additional experience and that there have been scientific developments in the intervening 12 years. All three reviewed facts and documents in the case and wrote that they now believe that Hill is mentally disabled.

The state questioned the credibility of the doctors' statements. These doctors met with Hill and reviewed extensive documentation in the case in 2000, but they haven't seen him since and didn't have significant new information in front of them during their recent review, the state argued. Therefore, it is not credible that they are able to refute the testimony they were so adamant about in 2000, the state argued.

The state has cited expert testimony and IQ tests that concluded Hill was not mentally disabled. Before trial, Hill's family members described him as "the leader of the family" and "a father figure," the state notes. He was not in special education classes and served in the Navy, where he received promotions, the state said.

The defense has referenced a state court judge's assessment that Hill was mentally disabled and a test that showed his IQ to be about 70. The defense also cited expert testimony that it is not unusual for someone who is mildly mentally disabled to be able to function at a satisfactory level in an environment as structured as the military. With the new statements from the three doctors last week, all doctors who examined him now agree that Hill is mentally disabled, Hill's defense argued.

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Associated Press writer Christina Almeida Cassidy in Atlanta contributed to this report.