Davis is scheduled to die Wednesday which is the fourth time his execution has been set in four years. He once came within two hours of being put to death. His attorneys say his legal appeals are exhausted and the chances of him winning another reprieve have dwindled.
However, supporters hope to convince Georgia's pardons board next week to spare his life.
The execution of Davis "risks taking the life of an innocent man and would be a grave miscarriage of justice," said former President Jimmy Carter, a Democrat from Georgia and death penalty opponent who wrote a letter on Davis' behalf.