The Georgia Department of Corrections has set the execution of Troy Anthony Davis for 7 p.m. on Sept. 21.

The agency set the time and date a day after a Chatham County judge signed a death warrant for Davis, who was convicted of killing an off-duty Savannah police officer in 1989. Also Wednesday, the state Board of Pardons and Paroles said it will hear, for the second time, Davis' bid for clemency. The board set its hearing for Sept. 19.

Because Davis' appeals are exhausted, the parole board appears to be his last chance to be spared from execution. In September 2008, the board denied an earlier request by Davis for clemency.

Davis, 41, was convicted of killing Officer Mark Allen MacPhail as MacPhail ran to the aid of a homeless man being pistol-whipped outside a Burger King.

The case has attracted international attention because a number of key prosecution witnesses either recanted or backed off their trial testimony. Other witnesses have come forward and said another man at the scene told them he was the actual killer.

Amnesty International, the human rights organization, called on the parole board to commute Davis' death sentence, saying doubts about Davis’ guilt have never been erased.

“The board stayed Davis’ execution in 2007, stating that capital punishment was not an option when doubts about guilt remained,” said Larry Cox, executive director for AIUSA. “Since then two more execution dates have come and gone, and there is still little clarity, much less proof, that Davis committed any crime. Amnesty International respectfully asks the Board to commute Davis’ sentence to life and prevent Georgia from making a catastrophic mistake.”

In August, a federal judge emphatically rejected Davis' claims that he was wrongly convicted. In a 172-page order, U.S. District Judge William T. Moore Jr. said Davis failed to prove his innocence during an extraordinary hearing in June ordered by the U.S. Supreme Court.

MacPhail, 27 and a father of two, was gunned down before he could draw his weapon. After the killing, Sylvester "Redd" Coles went to the police with his lawyer and told them he and Davis were at the scene. At trial, he testified he was fleeing the scene when shots were fired, leaving Davis as the culprit. Coles denied being the triggerman.

At the June hearing, Davis' lawyers wanted to call witnesses who had given sworn statements that Coles had told them after the trial he was the actual killer. But Moore did not allow these witnesses to testify because Davis' lawyers did not subpoena Coles to testify. If they had, the judge said, he could have tested the validity of Coles' alleged confessions.

If Coles had in fact confessed to these witnesses, Moore suggested there could be an explanation --"he believed that his reputation as a dangerous individual would be enhanced if he took credit for murdering Officer MacPhail." Davis failed to prove the alleged confessions were truthful, Moore noted.

Of the seven witnesses Davis' legal team say recanted their trial testimony, "only one is a meaningful, credible recantation." The value of this recantation -- given by a jailhouse snitch who testified Davis told him he killed MacPhail -- is diminished because it was already clear the witness testified falsely at trial, the judge said.

Moore answered one question posed to him by the U.S. Supreme Court. He found that executing an innocent person would violate the Eighth Amendment's ban against cruel and unusual punishment.

"However, Mr. Davis is not innocent," the U.S. district judge wrote in August.

Chatham County Superior Court Judge Penny Freesemann signed the death warrant Tuesday.

_  Staff writer Christopher Seward contributed to this report

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