After hearing exhaustive pleas both from Troy Davis supporters and the family of the man he was convicted of killing, the Georgia Board of Pardons and Paroles denied an 11th-hour clemency plea Tuesday, clearing the way for Mr. Davis's execution on Wednesday.

Pope Benedict, President Carter, and former FBI head William Sessions were among nearly 700,000 people around the world who campaigned, via signatures and testimony, that Mr. Davis's life be spared after seven of nine witnesses to the 1989 murder of off-duty Savannah, Ga., police officer Mark MacPhail changed or recanted their testimony in recent years.

The parole board appeal was a last-ditch effort for Davis after the Supreme Court, in a highly unusual move, demanded a district court review of the case last year. In the end, the review found that new evidence and changes in witness testimony didn't substantially affect the validity of the original 1991 murder conviction.

After three hours of testimony on Monday, Davis's lawyers said they believed they had demonstrated “substantial doubt” that Davis was the triggerman in the shooting of Mr. MacPhail, a former Army Ranger and young father, outside a Burger King in Savannah, Ga. One piece of new evidence included testimony that a different man at the scene later confessed he pulled the trigger.

But MacPhail's family, including his wife, told the clemency board that “it's time for justice.” Joan MacPhail-Harris, his wife, told reporters that Davis's claim of innocence was “a lie.”

Because of its high profile and byzantine journey through the US death penalty system, the Troy Davis case has been seen by some legal experts as a bellwether case for a justice system that sets a high bar for death row inmates trying to prove their innocence.

“Davis could not clearly establish that he was actually innocent,” despite dramatic reversals in witnesses' stories and new questions about a key ballistics test, says Russell Covey, a law professor at Georgia State University, in Atlanta.

No conclusive physical evidence tied Davis to the crime and he has always maintained he was innocent.

“I don't know if there are any other cases that are comparable given the sheer quantity of evidence of innocence or at least evidence that has thrown the credibility of the jury into a greater sort of doubt than what's come up in this case," Mr. Covey added.

Davis declined to order a special last meal. He will be served what's on the menu at the Georgia state prison in Jackson before his execution Wednesday: grilled cheeseburger, oven-browned potatoes, baked beans, coleslaw, cookies and a grape beverage.