A US parole board has denied clemency to Troy Davis, clearing the way for his execution today in a case that has become an international cause celebre for death penalty opponents.

Mr Davis was convicted of shooting dead an off-duty police officer who intervened in a brawl in a parking lot in Savannah, Georgia in 1989, but there was no physical evidence and several witnesses later recanted their testimony.

The campaign to spare his life drew high-profile support from former US President Jimmy Carter and Pope Benedict XVI, helping Mr Davis escape three previous dates with death during more than two decades of legal maneuvering.

All avenues now appear exhausted as Georgia’s governor does not have the power to stay executions and experts said any last-minute filings to the state courts or the US Supreme Court would likely prove unsuccessful.

The Georgia State Board of Pardons and Paroles considered the Davis appeal on Monday in the state capital Atlanta and deliberated overnight before announcing its decision. “The board denied clemency,” a spokesman said yesterday.

Barring an unexpected turn of events, Mr Davis will be put to death by lethal injection at 2300 GMT today at a prison in Jackson, south of Atlanta, with the victim’s widow and children looking on. “I am very convinced that he is guilty,” Anneliese MacPhail, the mother of the slain police officer, Mark MacPhail, told CNN. “I will never have closure. But I may have some peace when he is executed.”

Mr MacPhail’s widow, Joan MacPhail-Harris, described efforts to keep Mr Davis from execution as a series of lies and said she and the couple’s children, who were toddlers at the time of his murder, would attend the execution.

“We are the true victims here,” she said.

But Mr Davis has repeatedly claimed his innocence and his supporters point to a corrupted justice system in the deep south, saying a black man was wrongly and hastily convicted of killing a white police officer.

“I am utterly shocked and disappointed at the failure of our justice system at all levels to correct a miscarriage of justice,” Mr Davis’s attorney Brian Kammer said as rights groups and abolitionists rushed to condemn the decision.