JACKSON, Georgia (CNN) -- Troy Anthony Davis has long said he didn't kill a Savannah, Georgia, police officer, and the U.S. Supreme Court will decide Tuesday whether to postpone his 7 p.m. ET execution.
Troy Anthony Davis, 39, says he did not kill a Georgia police officer; he is to die Tuesday.
Davis, 39, was convicted in 1991 of killing Officer Mark MacPhail as MacPhail responded to an altercation in a Burger King parking lot.
Seven of the nine witnesses who initially testified that Davis was the killer have recanted. There was no physical evidence presented at his trial, and no weapon was found.
But Davis' petitions for a new trial have been denied.
If Davis is executed by lethal injection, he will be the 43rd inmate put to death by the state since 1973.
On Tuesday, Davis refused his last meal, according to the Georgia Department of Corrections, which will still provide him with macaroni and cheese, pinto beans, green beans, lettuce and tomato salad, corn bread, fruit cobbler and tea.
Davis had visitation with family members until 3 p.m. Tuesday and is undergoing a routine physical. At 4 p.m., he will be offered his last meal, followed by an offer to make a recorded last statement at 5 p.m.
According to the Department of Corrections Office of Public Affairs, Davis will be offered ativan, a mild sedative, at 6 p.m. and will be executed one hour later. His remains will then be transported to the Georgia Bureau of Investigation's crime lab for a routine autopsy before being released to his family.
Many have asked Georgia to grant Davis a new trial: celebrities like Susan Sarandon, Harry Belafonte and the Indigo Girls; world leaders such as former President Carter, Archbishop Desmond Tutu and Pope Benedict XVI; and former and current U.S. lawmakers like Bob Barr, Carolyn Moseley Braun and John Lewis.
Amnesty International has issued a 39-page report questioning his conviction, and protesters have been gathering at the Georgia Capitol in Atlanta this week. Davis is scheduled to be executed at the Georgia Diagnostic and Classification Prison in Jackson.
MacPhail's mother, Anneliese MacPhail of Columbus, said last week that she is "disgusted" by the calls to spare Davis' life and is not convinced by Davis' supporters' claims that there is a more likely suspect.
On Tuesday, Anneliese MacPhail said, "There is no possibility he's innocent, not according to what's been said in court."
"Troy Davis was judged by his peers. All the courts have found him guilty. It was proven he was guilty. Please let us have some peace. Let Mark rest in peace. Let justice be done," she said.
Davis' sister, Martina Correia, said she was sleepless Monday night and was spending Tuesday at his side. She said she planned to stay until prison officials told her to leave at 3 p.m.
"We are still holding on to hope," she said Tuesday morning. "We still hope the U.S. Supreme Court will look into my brother's case and give some relief. We will have a lot of family time with him and recall old times and pray together."
The Georgia Supreme Court turned down the plea for a stay in Davis' execution Monday, saying the U.S. Supreme Court "properly has jurisdiction over Davis' pending petition."
The Supreme Court called an emergency session to hear the petition.
Davis was convicted of MacPhail's 1989 murder largely on the testimony of nine witnesses.
"When you only have eyewitness testimony and you have no physical evidence, people have fallacies and people make mistakes," Correia said.
Davis' lawyers and supporters say this is a case of mistaken identity. Seven of the nine trial witnesses have changed their statements, saying they were mistaken, they feared retribution from the man they say actually killed MacPhail or that police pressured them into fingering Davis.
During the trial, witnesses said Davis and two other men were harassing a homeless man and followed him across the street from a parking lot at the Greyhound bus station in Savannah.
MacPhail was off-duty. He saw the skirmish and ran over to break up the fight. MacPhail was shot, and witnesses told police Davis fired the two shots that killed him.
A manhunt ensued. Davis surrendered nine days later.
Monty Holmes is one of the witnesses who said Davis was the culprit. He has changed his story and alleges that police coerced him.
"They were trying to get to me to say that he did it, but I know he didn't do it," Holmes said last year at a rally for Davis.
Savannah police Maj. Everett Ragan headed the MacPhail investigation. He denies allegations of coercion and said he doesn't believe the witnesses who have changed their stories.
Shortly before Davis was scheduled to be executed last year, Ragan told CNN, "There is no doubt in my mind we arrested the right man."
The Georgia Supreme Court also was unimpressed with the witnesses' new stories. In affirming the trial court's judgment in a 4-3 decision, the majority said that the witnesses' new testimony failed to meet the necessary benchmark: that their original testimony "in every material part is purest fabrication."
The court also was unconvinced by allegations that one of the men Davis was with that night, Sylvester "Red" Coles, killed MacPhail.
In a telephone interview in 2007, Davis acknowledged that he never told police that Coles killed MacPhail.
"I didn't because I didn't want to be a snitch," Davis said. "Yes, I know that's stupid."
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."
CNN's Tristan Smith and Gabriel Falcon contributed to this report.