Seven of the nine witnesses who gave evidence at Davis's trial in 1991 have recanted or changed their testimony.
Davis, 42, has repeatedly claimed his innocence and his supporters say the evidence supports that. No murder weapon was ever found, no DNA evidence or fingerprints tie Davis to the crime, and other witnesses have since said the murder was committed by another man -- a witness who testified against Davis.
The case has become internationally famous as the face of what critics call a corrupted justice system in the deep US south, with a black man wrongly and hastily convicted of killing a white officer.
The US Supreme Court became involved in 2009 and ordered a federal judge in Savannah to convene a hearing to consider new evidence.
In August 2010, however, a US District Court in Georgia ruled that Davis had failed to prove his innocence and denied him a new trial. The top US court turned down a subsequent appeal.
Davis is scheduled to die by lethal injection next week at a prison in Jackson, Georgia, south of Atlanta, barring any late decision on clemency. The parole board is made up of five members and it takes just a simple majority to decide a case