DEATH row prisoner Troy Davis has been executed in one of the most controversial American capital punishment cases in years.
Davis, 42, was put to death by lethal injection after a last minute appeal to the US Supreme Court failed, and his request to take a polygraph test was also turned down.
The appeal to the US Supreme Court led to a temporary delay of more than three hours.
Davis maintained his innocence to the end, saying: “I did not have a gun. For those about to take my life, may God have mercy on your souls. May God bless your souls.”
According to those who witnessed the execution Davis addressed some comments to the family of his victim while he was strapped to the gurney.
He told them: "I did not personally kill your son, father, brother.” He also asked his supporters to “dig deeper” into the case so they could “find the real truth.”
Davis was pronounced dead at 11.08pm local time.
Supporters held vigils outside the maximum security prison in Jackson, Georgia, the White House in Washington DC, and US embassies in London and Paris.
Davis had spent two decades on death row after being convicted of the 1989 killing of Mark MacPhail, an off-duty police officer who was working as a security guard in Savannah, Georgia.
Mr MacPhail, 27, was shot dead when he rushed to help a homeless man who was being pistol whipped in a Burger King car park in an argument over a beer.
Witnesses placed Davis at the scene and identified him as the gunman. Shell casings found in the car park were linked to an earlier shooting that he was convicted of.
But the murder weapon was never found and there was no other physical evidence, such as blood or DNA, to tie Davis to the crime. His lawyers claimed he was a victim of mistaken identity.
Seven of nine witnesses who gave evidence against him later recanted all or part of their testimony, while others have claimed that another man confessed to the killing. Some jurors have since changed their minds about his guilt.
A last ditch appeal by Davis's lawyers questioned the ballistics evidence in the case but was turned down by the five-member Georgia Board of Pardons.
Davis had received support from high profile figures including former President Jimmy Carter, Pope Benedict XVI and former FBI Director William Sessions. Nearly one million people signed a petition to the pardons board.
But the murder conviction was repeatedly upheld by state and federal courts.
One judge dismissed new evidence as "largely smoke and mirrors."
Last year, the US Supreme Court ordered a highly unusual hearing into the case and a federal judge, in a 150-page ruling, upheld the verdict and sentence.
Davis spent his last hours praying and talking to his family and supporters.
He declined an offer of a special last meal.
Outside the prison where he was put to death 200 supporters gathered.
Speaking before the execution his sister Martina Correia, who is battling breast cancer and in a wheelchair, said: "Troy Davis has impacted the world.
They say 'I am Troy Davis' in languages he can't speak." His lawyer Stephen Marsh said: "Such incredibly flawed eyewitness testimony should never be the basis for an execution." Veteran civil rights leader Rev Al Sharpton said: "This is an outrage. No one can execute a man with no physical evidence." But Mr MacPhail's widow, Joan MacPhail-Harris, said: "He has had ample time to prove his innocence. And he is not innocent." Earlier, White House Press secretary Jay Carney issued a statement saying that although President Barack Obama "has worked to ensure accuracy and fairness in the criminal justice system," it was not appropriate for him "to weigh in on specific cases like this one, which is a state prosecution."