Troy Davis will be executed as planned by lethal injection after the Georgia Board of Pardons and Paroles on Tuesday denied clemency for the death row inmate convicted of murdering police officer Mark MacPhail in 1989.

Steve Hayes, a spokesman for the Board of Pardons and Paroles, told The Associated Press that the five-member panel decided to reject Davis' request for clemency after it heard hours of testimony from his supporters and prosecutors. Davis is scheduled to die on Wednesday.

The victim's mother, Anneliese MacPhail, has said Davis' death would bring her peace. I think I finally will have peace of mind, she said. When it is over I can close that book and I know Mark can rest in peace, too.

Amnesty International and the NAACP have called on the pardons board to reconsider their decision. This is the fourth time in four years Davis' execution has been scheduled by Georgia officials, The AP said.

Davis has maintained his innocence since being accused of the crime and has gathered high-profile support from such figures as former President Jimmy Carter and Pope Benedict XVI. His advocates have asked for clemency, noting that several witnesses in the case have signed affidavits withdrawing their testimony, stating that police coerced them into accusing the 42-year-old man.

Defense attorney Jason Ewart has said previously the pardons board was probably Davis' last option.

I am utterly shocked and disappointed at the failure of our justice system at all levels to correct a miscarriage of justice, Brian Kammer, one of Davis's attorneys, to the UK Guardian following the pardons board's decision.

Davis was 19 when he was arrested as the suspect who shot and killed Mark MacPhail, 27, who was moonlighting as a security guard outside a Savannah bus station on Aug. 19, 1989. MacPhail was shot dead while rushing to help a homeless man who was being attacked, according to reports.

Davis was convicted in 1991 based on the testimony of nine witnesses who all said they'd seen him pull the trigger. Davis said he was at the scene, but said another man, Sylvester Coles, attacked the homeless man and also shot MacPhail when he tried to stop it.

The murder weapon is yet to be found, according to the Guardian, and there's was never any DNA or other forensic evidence.

Seven of the nine witnesses have come forward since the trial and recanted their testimony. The witnesses have said police pressured them in to implicating Davis. Others have also come forward, saying they've heard Coles confess to killing the police officer.

The Atlanta Journal-Constitution has reported that Quiana Glover, of Savannah, has also said she was at a friend's house in June 2009 when Coles was there drinking heavily and revealed he was the one who killed MacPhail.

Amnesty International said the state's Board of Pardons and Paroles must reconsider their decision to deny clemency for Davis.

This is a huge setback for human rights in the USA, where a man who has been condemned under dubious evidence is to be executed by the state, said Salil Shetty, Amnesty International's Secretary General, in a statement. Even at this late stage, the board must reconsider its decision,

The decision by Georgia's Board of Pardons and Paroles to reject Troy Davis' appeal for clemency is obviously at odds with their 2007 decision when they counseled against execution if there was 'doubt as to the guilt of the accused' Shetty added. Even if members of the Board were convinced that there was no doubt, many other people have not been so persuaded.

Clearly, the U.S. capital justice system is capable of making mistakes, said Shetty. The persistent doubts that have plagued the Troy Davis case point to a fundamental flaw of the death penalty. It is irrevocable - and in the USA, the death penalty is also marked by arbitrariness, discrimination and error.