ATLANTA » Convicted cop killer Troy Davis is scheduled to be executed today for a crime he says he did not commit.

Vigils outside Georgia’s death chamber were set. Protests were planned. Davis’ attorneys said he was willing to take a polygraph test if the pardons board would consider its results. And they didn’t rule out filing one last legal appeal, though they know it’s a long shot.

In Europe, where the planned execution has drawn widespread criticism, legislators and activists were making a last-minute appeal to the state of Georgia to refrain from executing Davis. Amnesty International and other groups planned a protest outside the U.S. Embassy in Paris later Wednesday.

Renate Wohlwend of the Council of Europe’s Parliamentary Assembly noted doubts raised about Davis’ conviction. She said that "to carry out this irrevocable act now would be a terrible mistake which could lead to a tragic injustice."

Davis is to be executed by injection at 7 p.m. 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 had been attacked.

Davis didn’t want a last meal. He planned to spend his final hours meeting with friends, family and supporters. According to an advocate who met with him late Tuesday, he was upbeat, prayerful and expected last-minute wrangling by attorneys.

Attorney Stephen Marsh said he had asked state prisons officials and the pardons board if they would allow a polygraph test. A prisons spokeswoman said she was unaware of the request and the pardons board didn’t immediately respond.

"He doesn’t want to spend three hours away from his family on what could be the last day of his life if it won’t make any difference," Marsh said.

Davis has received support from hundreds of thousands of people, including a former FBI director, former President Jimmy Carter and Pope Benedict XVI. Some of his backers resorted to urging prison workers to strike or call in sick today, and they considered a desperate appeal for White House intervention.

The U.S. Supreme Court gave him an unusual opportunity to prove his innocence last year, but his attorneys failed to convince a judge he didn’t do it. State and federal courts have repeatedly upheld his conviction.

Prosecutors have no doubt they charged the right person, and MacPhail’s family lobbied the pardons board Monday to reject Davis’ clemency appeal. The board refused to stop the execution a day later.

"He has had ample time to prove his innocence," said MacPhail’s widow, Joan MacPhail-Harris. "And he is not innocent."

Spencer Lawton, the district attorney who secured Davis’ conviction in 1991, said he was embarrassed for the judicial system that the execution has taken so long.

"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," said Lawton, who retired as Chatham County’s head prosecutor in 2008. "The good news is we live in a civilized society where questions like this are decided based on fact in open and transparent courts of law, and not on street corners."

Davis supporters said they will push the pardons board to reconsider his case. They also asked Savannah prosecutors to block the execution, although Chatham County District Attorney Larry Chisolm said in a statement he was 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.

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, they say Davis had a smirk on his face as he shot the officer to death.

Witnesses placed Davis at the crime scene and identified him as the shooter. Shell casings were linked to an earlier shooting 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 found.

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

The state initially planned to execute him 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 two hours before he was to be executed. And a federal appeals court halted another planned execution a few months later.

Over the years, Davis has picked up high-profile support from a host of dignitaries and dozens of federal lawmakers. Conservative figures have also advocated on his behalf, including former U.S. Rep. Bob Barr, ex-Justice Department official Larry Thompson and one-time FBI Director William Sessions.

The U.S. Supreme Court granted Davis a hearing to prove his innocence, the first time it had done so for a death row inmate in at least 50 years. At that June 2010 hearing, two witnesses testified that they falsely incriminated Davis at his trial when they said Davis confessed to the killing. Two others told the judge 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 them. He said the evidence presented at the hearing wasn’t nearly enough to prove Davis is innocent and validate his request for a new trial. He said while Davis’ "new evidence casts some additional, minimal doubt on his conviction, it is largely smoke and mirrors."