Coles has never been charged with the murder and, according to court documents, has testified at least twice that he was not the killer.
Davis' lawyers claim that there are other people who saw what happened that night. Those witnesses have never testified in court but have submitted affidavits, the attorneys say.
On Monday, the Georgia Board of Pardons and Paroles said it typically does not comment on clemency appeals but defended itself because Davis' case has received such widespread attention. The statement noted that the board postponed Davis' execution last year and has studied the case for a year.
"After an exhaustive review of all available information regarding the Troy Davis case and after considering all possible reasons for granting clemency, the board has determined that clemency is not warranted," the statement said.
Anneliese MacPhail said she has attended every court hearing for Davis and made an appearance before the parole board this month.
But if the execution moves forward, the slain officer's mother will not accompany her grandson -- MacPhail's son, Mark Jr. -- to Jackson to watch Davis die. MacPhail's wife, Joan, will not attend the execution, either, she said.
"This was my son," Anneliese MacPhail said. "You can't imagine the hell we have been through."
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