JACKSON, Ga. — The United States Supreme Court rejected a last-ditch request to step in late Wednesday to stay the Georgia execution of Troy Davis, who was convicted of gunning down a Savannah police officer 22 years ago, after Mr. Davis filed an eleventh-hour plea Wednesday with the high court.
His execution, by lethal injection, had been set to begin at 7 p.m., but Georgia prison officials waited for the court’s decision late into the evening. It took the court more than four hours to issue its one-sentence order.
For Mr. Davis’s family members, who had gathered on the lawn near the entrance of the prison, unbearably tense moments of waiting dissolved into tears and prayer upon hearing the court's decision.
"We're calling on everyone to stay calm," said Benjamin T. Jealous, president of the N.A.A.C.P.
Mr. Davis’s lawyers had asked the court to examine what they said were “substantial constitutional errors” in the murder trial.
Throughout the evening, police officers in riot gear kept what appeared to be about 500 protesters at bay across the state highway from the prison entrance.
A dozen supporters of the death penalty, including people who knew the family of the slain officer, Mark MacPhail, sat quietly, separated from the Davis family and their supporters by a stretch of lawn and rope barriers.
The appeal to the Supreme Court was one of several last-ditch efforts by Mr. Davis on Wednesday. Earlier in the day, an official of the N.A.A.C.P. said that the vote by the Georgia parole board to deny clemency to Mr. Davis, who is black, was so close that he hoped there might still be a chance to save him from execution.
Edward O. DuBose, president of the Georgia chapter, said the organization had “very reliable information from the board members directly that the board was split 3 to 2 on whether to grant clemency.”
“The fact that that kind of division was in the room is even more of a sign that there is a strong possibility to save Troy’s life,” he said.
The N.A.A.C.P said it had been in contact with the Department of Justice on Wednesday, in the hope that the federal government would intervene on the basis of civil rights violations, meaning irregularities in the original investigation and at the trial.
Earlier in the day, his lawyers asked the state for another chance to spare him: a lie detector test.
But the Georgia State Board of Pardons and Parole, which on Tuesday denied Mr. Davis’s clemency after a daylong hearing Monday, quickly responded that there would be no reconsideration of the case, and the polygraph test was abandoned.
Mr. Davis’s supporters were also reaching out to the prosecutor in the original case, asking that he persuade the original judge to rescind the death order. Mr. Jealous was trying to ask President Obama for a reprieve.
The Innocence Project, which has had a hand in the exoneration of 17 death-row inmates through the use of DNA testing, sent a letter to the Chatham County district attorney, Larry Chisolm, urging him to withdraw the execution warrant against Mr. Davis.
Mr. Davis, now 42, was convicted of the 1989 shooting of Officer MacPhail, who was working a second job as a security guard. A homeless man called for help after a group that included Mr. Davis began to assault him, according to court testimony. When Officer MacPhail went to assist him, he was shot in the face and the heart.
Since then, Mr. Davis has walked to the brink of execution three other times.
With this most recent execution date, Mr. Davis became an international symbol of the battle over the death penalty and racial imbalance in the justice system.
His conviction came after testimony by some witnesses who later recanted and on the scantest of physical evidence, adding fuel to those who relied increasingly on the Internet to rally against executions and to question the validity of eyewitness identification and of the court system itself.
“It harkens back to some ugly days in the history of this state,” said the Rev. Raphael Warnock of Ebenezer Baptist Church, who visited Mr. Davis on Monday.
But for the family of the slain officer, and countless others who believe that two decades’ worth of legal appeals and Supreme Court intervention is more than enough to ensure justice, it is not an issue of race but of law.
Inside the prison, Officer MacPhail’s widow and two grown children waited to see if the 22-year-long process would end with Mr. Davis’s death.
Officer MacPhail’s widow, Joan MacPhail-Harris, said calling Mr. Davis a victim was ludicrous.
“We have lived this for 22 years,” she said Monday. “We are victims.”
She added: “We have laws in this land so that there is not chaos. We are not killing Troy because we want to.”
Mr. Davis, who refused a last meal, was in good spirits and prayerful, said Wende Gozan Brown, a spokeswoman for Amnesty International, who visited him on Tuesday. She said he had told her his death was for all the Troy Davises who came before and after him.
“I will not stop fighting until I’ve taken my last breath,” she recounted him as saying. “Georgia is prepared to snuff out the life of an innocent man.”
The case has been a slow and convoluted exercise in legal maneuvering and death penalty politics.
This is the fourth time Mr. Davis has faced the death penalty. The state parole board granted him a stay in 2007 as he was preparing for his final hours, saying the execution should not proceed unless its members “are convinced that there is no doubt as to the guilt of the accused.” The board has since added three new members.
In 2008, his execution was about 90 minutes away when the Supreme Court stepped in. Although the court kept Mr. Davis from execution, it later declined to hear the case.
This time around, the case catapulted into the national consciousness with record numbers of petitions — more than 630,000 — delivered to the board to stay the execution, and a list of people asking for clemency included former President Jimmy Carter, Archbishop Desmond Tutu, 51 members of Congress, entertainment figures like Cee Lo Green and even some death penalty supporters, including William S. Sessions, a former F.B.I. director.