ATLANTA — Yet another appeal denied, Troy Davis was left with little to do Tuesday but wait to be executed for a murder he insists he did not commit.

He lost his most realistic chance to avoid lethal injection on Tuesday, when Georgia's pardons board rejected his appeal for clemency. As his scheduled 7 p.m. Wednesday execution neared, his backers resorted to far-fetched measures: urging prison workers to strike or call in sick, asking prosecutors to block the execution -- even considering a desperate appeal for White House intervention.

He has gotten support from hundreds of thousands of people, including a former FBI director, former President Jimmy Carter and Pope Benedict XVI, and a U.S. Supreme Court ruling gave him an unusual opportunity to prove his innocence last year. State and federal courts, however, repeatedly upheld his conviction for the 1989 killing of Mark MacPhail, an off-duty police officer who was working as a security guard in Savannah when he was shot dead rushing to help a homeless man who was being attacked.

Davis' attorneys say he was convicted based on flawed testimony that has been largely recanted by witnesses, but prosecutors and MacPhail's relatives say they have no doubt the right man is being punished.

"Justice was finally served for my father," said Mark MacPhail Jr., who was an infant when his father was gunned down. "The truth was finally heard."

As Davis' attorneys considered filing another appeal, his supporters planned vigils and rallies around the world. Nearly 1 million signed a petition seeking clemency, according to Amnesty International.

"We've been praying about it and with God on our side anything can happen," DeJaun Correia-Davis, the condemned man's 17-year-old nephew, told a rally of hundreds in front of the Georgia Capitol late Tuesday. "Let this be a case that not only highlights the death penalty but will hopefully be a big part in bringing it to an end."

Georgia initially planned to execute Davis in July 2007, but the pardons board granted him a stay less than 24 hours before he was to die. The U.S. Supreme Court stepped in a year later and halted the lethal injection just two hours before he was to be executed. And a federal appeals court halted another planned execution a few months later.

This time, state officials are confident this lethal injection will be carried out. Georgia's governor does not have the power to grant condemned inmates clemency. Davis supporters are calling on Chatham County District Attorney Larry Chisolm to block the execution. But the prosecutor said in a statement Tuesday he's powerless to withdraw an execution order for Davis issued by a state Superior Court judge.

"We appreciate the outpouring of interest in this case; however, this matter is beyond our control," Chisolm said.

Spencer Lawton, the prosecutor who secured Davis' conviction in 1991, said he has no doubt he is guilty.

"What we have had is a manufactured appearance of doubt which has taken on the quality of legitimate doubt itself. And all of it is exquisitely unfair," Lawton said.

MacPhail was shot to death Aug. 19, 1989, after coming to the aid of Larry Young, a homeless man who was pistol-whipped in a Burger King parking lot. Prosecutors say Davis was with another man who was demanding that Young give him a beer when Davis pulled out a handgun and bashed Young with it. When MacPhail arrived to help, prosecutors say Davis had a smirk on his face when he shot the officer to death.

Witnesses placed Davis at the crime scene and identified him as the shooter. Shell casings were linked to a shooting hours earlier that Davis was convicted of. There was no other physical evidence. No blood or DNA tied Davis to the crime and the weapon was never located.

Davis' attorneys say seven of nine key witnesses who testified at his trial have disputed all or parts of their testimony.

Quiana Glover, who did not testify at the original trial, said one of the witnesses who did not recant told her he was the real shooter. That man, who was with Davis that night, could not be reached for comment on Monday and Tuesday, and did not answer his door this week when a reporter visited.

"Justice should be served, but it should be served to the right man," said Glover, who urged the pardons board to grant clemency Monday. "There's no evidence against this young man."

As advocacy groups highlighted the case, a growing number of dignitaries became involved. A host of conservative figures are among those who have advocated on his behalf, including former U.S. Rep. Bob Barr, ex-Justice Department official Larry Thompson and one-time FBI Director William Sessions.

Their concerns helped prod the U.S. Supreme Court to grant Davis a hearing in Savannah to prove his innocence, a nearly unprecedented move. Two witnesses at the June 2010 hearing testified that they falsely incriminated Davis at his trial, and two others told the judge that the man with Davis that night later said he shot MacPhail.

Prosecutors, though, argued that Davis' lawyers were simply rehashing old testimony that had already been rejected by a jury. And they said no trial court could ever consider the hearsay from the other witnesses who blamed the other man for the crime.

U.S. District Judge William T. Moore Jr. sided with prosecutors and rejected Davis' request for a new trial. He said that while "new evidence casts some additional, minimal doubt on his conviction, it is largely smoke and mirrors."

On Tuesday, Davis was spending his last quiet hours with friends, family and supporters, said Wende Gozan Brown, an Amnesty International staffer who visited him.

"He said he's in good spirits, he's prayerful and he's at peace. But he said he will not stop fighting until he's taken his last breath. And he said Georgia is about to snuff out the life of an innocent man," she said.

His supporters are exploring other options. State Sen. Vincent Fort called on all but a skeleton staff of prison workers to strike on Wednesday.

The National Association for the Advancement of Colored People said it was considering asking President Barack Obama to intervene, a move that legal experts considered unlikely.

MacPhail's family, which urged the pardons board on Monday to reject Davis' clemency bid, said his execution will bring them peace.

"That's what we wanted, and that's what we got," said MacPhail's mother, Anneliese MacPhail. "We wanted to get it over with, and for him to get his punishment."