Troy Davis, a convicted murderer, has been executed in the US state of Georgia after the US Supreme Court denied a last minute stay which would have stopped the lethal injection.
The high court had asked Georgia to stop the execution just before 7pm, when it had been planned.
After an hours-long review, the court unanimously ceded their recommendation to an earlier decision by Georgia's Board of Pardons and Paroles to execute Davis, an African American who was sentenced to death in 1991 for the killing of Mark MacPhail, a 27-year-old white police officer.
The execution occurred at 11:08pm local time (03:08 GMT) on Wednesday.
According to witnesses who spoke at a press conference immediately after Davis was given a cocktail of drugs that ended his life, Davis's last words to those administering the execution were: "May God have mercy on your souls and may God bless your souls."
They said he also told the family of the slain officer that he was innocent - a claim he maintained since his arrest.
Advocates for Davis had collected more than 650,000 petition signatures begging the state of Georgia to let Davis live beyond Wednesday, and haf received support from people as widely reaching as the pope, a former FBI director, congressional representatives and Hollywood stars.
The support was so wide reaching because of claims that there was "too much doubt" in the case against Davis.
Seven of the nine witnesses who testified against Davis in his 1991 trial later changed their testimony, and two witnesses said they saw another man - who originally blamed Davis for the killing - pull the trigger.
Georgia's pardon board
The previous day, Georgia's board of pardons rejected a last-ditch clemency bid from Davis.
The five-member Board of Pardons and Paroles spent Monday hearing from Davis's supporters, prosecutors and the family of the victim before issuing its verdict on Tuesday.
"The board has considered the totality of the information presented in this case and thoroughly deliberated on it, after which the decision was to deny clemency," a written statement said. It did not disclose the vote breakdown.
The victim's widow and adult children were due to attend the execution, while Davis' family was not allowed inside the facility.
"We've been here three times before," Anneliese MacPhail, the mother of the slain police officer, said. "We are ready to close this book and start our lives. This has been a long haul."
Davis had captured worldwide attention after his supporters raised concerns that he was a victim of mistaken identity.
Several of the witnesses who helped convict Davis at his 1991 trial later backed off their testimony or
recanted. Others who did not testify say another man at the scene admitted to the shooting.
MacPhail, the victim, had been working nights as a security guard when he intervened to defend a homeless man in a brawl in a Burger King car park in Savannah, Georgia and was shot in the heart and the head at point-blank range.
There was no physical evidence tying Davis, who was 20 years old at the time of the murder, to the crime.
Davis' execution was the fourth in four years in the state of Georgia.