A Georgia parole board has rejected a final appeal from U.S. death row inmate Troy Davis, whose case has drawn international attention because of claims he was wrongly convicted.

Davis is set to be executed by lethal injection Wednesday in the southern state of Georgia for the 1989 shooting death of a police officer. This is the fourth time in four years the state has tried to execute him.

The five-member board released its final decision in a statement Tuesday morning after hours of hearings from Davis' supporters and prosecutors.

His case has drawn international attention for having no physical evidence linking him to the crime and since seven of the nine witnesses who helped convict Davis have retracted or recanted testimony. The Supreme Court has not reviewed the case, but took a rare step in 2009 ordering a Georgia appeals court to review new evidence in the case. Davis was denied another trial and the Supreme Court did not review the appeal.

Pope Benedict, former U.S. president Jimmy Carter, Archbishop Desmond Tutu, a former FBI director and conservative Georgia politicians are among those who have questioned Davis' guilt and advocated on his behalf. Thousands of people around the world have rallied in recent day and millions have signed petitions to stop Davis' execution.

Amnesty International released a statement Tuesday saying Davis' execution under an “enormous cloud of doubt about his guilt is an outrageous affront to justice.” Amnesty Executive Director Larry Cox called the decision “unconscionable.”

The family of slain police officer Mark MacPhail stand by the court's ruling that Davis is guilty. MacPhail's widow says Davis has had “ample time to prove his innocence.”