Troy Davis execution set for September 21

In the more than two decades that he has been in jail for the murder of white police officer Mark Allen MacPhail, Davis, an African-American, has maintained his innocence.

The Georgia superior court ordered the execution of Davis for 7:00 pm (2300 GMT) on September 21. Amnesty International USA (AIUSA) called on the Georgia Board of Pardons and Paroles to grant clemency, insisting that "proceeding with the execution would be unconscionable, especially as doubts about Davis\'s guilt have never been erased."

Since the original execution date in 2007 was stayed, because capital punishment "was not an option when doubts about guilt remained," said AIUSA director Larry Cox, there remains "little clarity, much less proof, that Davis committed any crime."

The human rights group urged the Georgia board overseeing the case to commute Davis\'s sentence to life in prison, and prevent the southern US state from making "a catastrophic mistake."

Davis has repeatedly said he did not kill MacPhail, and seven out of nine witnesses who gave evidence at his trial in 1991 have recanted or changed their testimony.

No murder weapon was ever found, no DNA evidence or fingerprints tie him to the crime, and other witnesses have since said the murder was committed by another man -- a state\'s witness who testified against him.

The case has became internationally famous as the face of what critics call a corrupted justice system in the US deep south, with an innocent black man wrongly and hastily convicted of killing a white officer.

With hundreds of thousands of signatures to petitions calling for leniency, celebrity backers including Nobel laureates ex-US president Jimmy Carter and Archbishop Desmond Tutu have also appealed to the board for clemency.

After Davis\'s lawyers exhausted all options for relief in the lower courts, they went to the US Supreme Court in 2009 seeking an \'original\' writ of habeas corpus, one that the high court issues without lower court involvement.

The Supreme Court had not issued an original writ of habeas corpus for nearly 50 years but in a landmark decision in August 2009, the justices ruled that Davis should be allowed to present to a district court judge what he claimed was exculpatory evidence that was not available during his 1991 trial.

In August 2010, however, the district court in Georgia ruled that Davis had failed to prove his innocence and denied him a new trial.

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