A long legal battle for Troy Davis could end next week in a death chamber in a Georgia prison.

Davis is scheduled to be executed on Sept. 21 for the murder of police officer Mark MacPhail in 1989 in Savannah. However, Davis has maintained his innocence.

His lawyers have been arguing that they can prove their client's innocence and have managed to spare him from three execution dates in the last four years, according to The Associated Press, and after a series of appeals that received special attention from the U.S. Supreme Court, Davis couldn't convince the courts to grant him a new trial.

Davis has almost exhausted his legal options and is facing death by injection Wednesday night.

MacPhail, 27, was operating as a security guard outside a Savannah bus station on Aug. 19, 1989, when he was shot and killed. He was rushing to help a homeless man who was being attacked, according to The AP.

Davis, who was 19 at the time, was arrested as the killer and eyewitness statements two years later influenced a jury to sentence him to death.

It was definitely not the Troy we knew, Davis's younger sister Kim told The AP. It was very, very shocking when it did happen. It kind of turned the family upside down.

Protest rallies in Atlanta against the judicial killing attracted thousands, and about 300 similar rallies were held worldwide ahead of a parole board hearing for the Davis, according to reports.

Davis' supporters claim his innocence, noting 10 witnesses in the case have signed affidavits withdrawing their testimony saying that police coerced them into accusing the 41 year old.

If I knew then what I know now, Brenda Davis, one of the jurors in the trial told CNN in a 2009 interview, Troy Davis would not be on Death Row. The verdict would be 'not guilty.'

The Georgia Board of Pardons and Paroles on Thursday got petitions with 663,000 names urging clemency, and it will convene on Monday to consider the case.

It is all that stands between Davis and execution.

But the slain officer's family told The AP they are confident Davis killed MacPhail.

His mother Anneliese MacPhail dismisses Davis' advocates, which includes the NAACP, Amnesty International, former President Jimmy Carter, and Pope Benedict XVI .

Anneliese MacPhail said they are ill-informed interlopers who have only prolonged her family's push for justice, according to The AP, and that she's cautiously confident that will end Wednesday.

I think I finally will have peace of mind, said Anneliese MacPhail, who lives in Columbus. When it is over I can close that book and I know Mark can rest in peace, too.

Also Read: Examining the Troy Davis Case: Is there Too Much Doubt? [VIDEOS]