Davis' supporters argue he was the victim of a rush to judgment by police seeking justice for the death of one of their own, as well as widespread racial prejudice in the criminal justice system. The Rev. Raphael Warnock, the senior pastor at Atlanta's Ebenezer Baptist Church, noted to CNN that several other inmates have been proven innocent in recent years.

"Unfortunately, tomorrow morning, it will be too late for an exoneration for Troy Davis," Warnock said.

Supporters argue that the original witnesses who testified against Davis were fearful of police and spoke under duress. Other witnesses also have since come forward with accounts that call Davis' conviction into question, according to his supporters.

According to prosecutors, Davis was at a pool party in Savannah when he shot a man, Michael Cooper, wounding him in the face. He then went to a nearby convenience store, where he pistol-whipped a homeless man, Larry Young, who'd just bought a beer, according to accounts of the case.

Prosecutors said MacPhail rushed to the scene to help, but wound up being shot three times by Davis. They said Davis shot the officer once in the face as he stood over him.

A jury convicted Davis on two counts of aggravated assault and one count each of possessing a firearm during a crime, obstructing a law enforcement officer and murder. The murder charge led to the death sentence.

MacPhail told CNN earlier this week that she didn't begrudge protesters their opinions. But she said they don't understand the facts of the case.

"To them the point is the death penalty. Ninety-nine percent have absolutely no idea who Troy Davis is or who Mark MacPhail was," she said. "They're just following their belief."

CNN's David Mattingly, Vivian Kuo and John Murgatroyd contributed to this report.