The U.S. Supreme Court  has refused to block the controversial execution of condemned Georgia inmate Troy Davis, which was delayed for several hours as the Court deliberated a stay.

The court did not comment on the order, which came after the Georgia pardons board and the state's Supreme Court rejected last-minute requests from Davis to spare his life. 

Davis, 42, was set to die at 7 p.m. ET for the 1989 murder of off-duty Savannah officer Mark MacPhail, who was killed while rushing to help a homeless man being attacked.

His lawyers have long argued Davis was a victim of mistaken identity, while prosecutors say they have no doubt that they charged the right person with the crime.

Davis' supporters had tried increasingly frenzied measures, urging prison workers to stay home and even posting a judge's phone number online, hoping people would press him to put a stop to lethal injection.

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"They say death row; we say hell no!" hundreds of protesters chanted outside the Jackson prison where Davis was to be executed. The crowd outside the prison swelled to more than 500 as night fell and a few dozen riot police stood watch.

The protests spanned the globe. Some 150 people gathered in Paris to voice their support for Davis. In Washington, D.C., dozens of protesters rallied outside the White House. Police arrested at least twelve.

The state Pardons and Paroles Board said in a statement Wednesday it would not review its decision to allow the execution to go forward.

Davis' lawyers had filed a late appeal Wednesday asking a local judge to block the execution over evidence they object to, but it was rejected by the judge and later by the Georgia Supreme Court. The motion argued that ballistic testing that linked Davis to the shooting was flawed. 

Davis was willing to take a polygraph test if the pardons board would consider its results, but that request was also denied early Wednesday. 

"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," said Attorney Stephen Marsh.

Davis had not requested a specific last meal and was offered a standard prison meal tray consisting of a cheeseburger, potatoes and slaw, which he did not eat, the Atlanta Journal & Constitution reports. He planned to spend his final hours meeting with friends, family and supporters. According to an advocate who met with Davis late Tuesday, he was upbeat, prayerful and expected last-minute wrangling by attorneys.

After winning three delays since 2007, Davis lost his most realistic chance at last-minute clemency this week when the state pardons board denied his request. 

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."

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.

It was first time the Supreme Court had given such an opportunity 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."

State and federal courts have repeatedly upheld his conviction.

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."

But 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.

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 Wednesday, and they considered a desperate appeal for White House intervention.

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.

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.

In Europe, where the planned execution has also drawn widespread criticism, politicians and activists were making a last-minute appeal to the state of Georgia to refrain from executing Davis. Amnesty International and other groups planned protests outside the U.S. Embassy in Paris and Amnesty also called a vigil outside the U.S. Embassy in London.

Parliamentarians and government ministers from the Council of Europe, the continent's human rights watchdog, called for Davis' sentence to be commuted. Renate Wohlwend of the Council's Parliamentary Assembly noted doubts raised about Davis' conviction by his supporters and said that "to carry out this irrevocable act now would be a terrible mistake which could lead to a tragic injustice."

Fox News' John Roberts and the Associated Press contributed to this report.