Updated at 3:54 p.m. ET
ATLANTA - Georgia's board of pardons rejected a last-ditch clemency bid from Troy Davis on Tuesday, one day before his scheduled execution, despite support from figures including an ex-president and a former FBI director for the claim that he was wrongly convicted of killing a police officer in 1989.
Davis is scheduled to die Wednesday at 7 p.m. EDT by injection for killing off-duty Savannah officer Mark MacPhail, who was shot dead while rushing to help a homeless man being attacked. It is the fourth time in four years that Davis' execution has been scheduled by Georgia officials.
"Justice was finally served for my father," said Mark MacPhail Jr., who was an infant when his father was gunned down. "The truth was finally heard."
The decision appeared to leave Davis with little chance of avoiding his execution date. Defense attorney Jason Ewart has said that the pardons board was likely Davis' last option, but he didn't rule out filing another legal appeal.
Kim Davis, the inmate's sister, declined immediate comment on the decision. But his supporters said they will push the pardons board to reconsider the case and urge prison workers to strike or call in sick on Wednesday to prevent Davis' execution. They also will push Savannah prosecutors to block the execution.
"This is a civil rights violation and a human rights violation in the worst way," said the Rev. Raphael Warnock, who spoke to the board on Davis' behalf on Monday. "This is Jim Crow in a new era. There's too much doubt for this execution to continue."
CBS News chief legal analyst Andrew Cohen described the denial of clemency as "routine."
"Parole boards almost never grant clemency, so this is not a surprise," Cohen said. "Now if Wednesday's execution is going to be halted it's going to have to come from the federal courts, and the U.S. Supreme Court in particular, which last week halted a Texas execution."
(At left, watch a "CBS Evening News" report on efforts to exonerate Davis)
"The Board members have not taken their responsibility lightly and certainly understand the emotions attached to a death penalty case," the five-person panel said in a statement.
Davis' lawyers have long argued Davis was a victim of mistaken identity. But prosecutors say they have no doubt that they charged the right person with the crime.
MacPhail was shot to death Aug. 19, 1989, after coming to the aid of Larry Young, a homeless man who was pistol-whipped in a Burger King parking lot. Prosecutors say Davis was with another man who was demanding that Young give him a beer when Davis pulled out a handgun and bashed Young with it. When MacPhail arrived to help, they say Davis had a smirk on his face when he shot the officer to death.
The National Association for the Advancement of Colored People said it was considering asking President Barack Obama to intervene. Obama cannot grant Davis clemency since Davis was convicted in state court, but could potentially halt the execution by asking for an investigation into a federal issue if one exists, according to Richard Dieter, executive director of the Death Penalty Information Center.
Dieter said he thought it was unlikely Obama would intervene.
The Rev. Al Sharpton, who plans to hold a vigil at the state prison in Jackson on Wednesday, called on supporters to urge Chatham County District Attorney Larry Chisolm to block the execution.
"This is probably the most egregious injustice I have seen in a long time, to set a precedent that a man can be executed when the evidence against him has mostly been recanted," said Sharpton. "It's unthinkable."
Chisolm's spokeswoman, Alicia Johnson, did not immediately return calls seeking comment Tuesday. But Chisolm has said it's unlikely he will seek to intervene.
"What stands between the defendant and execution is the Board of Pardons and Paroles," Chisolm said on Friday. "And I think whatever decision they make in the case will probably be the final decision."
Davis has captured worldwide attention because of the doubt his supporters have raised over whether he killed MacPhail. Several of the witnesses who helped convict Davis at his 1991 trial have backed off their testimony or recanted. Others who did not testify say another man at the scene admitted to the shooting.
The U.S. Supreme Court even granted Davis a hearing last year to prove his innocence, the first time it had done so for a death row inmate in at least 50 years. But in that June 2010 hearing, Davis couldn't convince a federal judge to grant him a new trial. The Supreme Court did not review his case. Federal appeals courts and the Georgia Supreme Court have upheld his conviction, leaving the parole board as his last chance.
MacPhail's relatives said they were relieved by the decision. "That's what we wanted, and that's what we got," said Anneliese MacPhail, the victim's mother. "We wanted to get it over with, and for him to get his punishment."