Lawyers for condemned US inmate Troy Davis say they have asked state officials to allow him to take a polygraph test before his scheduled execution.
Lawyer Stephen Marsh said that they had asked state prison officials and the pardons board for the test.
Davis is scheduled to die on Wednesday night, US time.
He has long claimed he is innocent of killing Mark MacPhail, an off-duty police officer working as a security guard in Savannah, Georgia. But state and federal courts have repeatedly upheld his conviction.
Prosecutors and Mr MacPhail’s relatives say they have no doubt the right man is being punished.
A prisons spokeswoman says she is unaware of the request and the pardons board didn’t immediately respond.
In a racially charged case that has become an international cause celebre for death penalty opponents, Davis, who is black, was convicted 20 years ago of the fatal 1989 shooting of 27-year-old white police officer Mr MacPhail, a married father of a two-year-old girl and an infant boy.
Mr MacPhail had been working nights as a security guard when he intervened in a brawl in a Burger King parking lot in Savannah, Georgia and was shot in the heart and the head at point-blank range.
There was no physical evidence tying Davis, who was 20 years old at the time of the murder, to the crime and several witnesses at his original trial later recanted their testimony.
During two decades of legal maneuvering, the campaign to spare his life drew high-profile support from former US president Jimmy Carter and Pope Benedict XVI, helping Davis escape three previous dates with death.
Davis, now 42, has always maintained his innocence and is a poster child for death penalty abolitionists who highlight doubts over his conviction and say the state of Georgia is about to execute an innocent man.
The five-member Georgia State Board of Pardons and Paroles spent Monday hearing from Davis’s supporters, prosecutors and the distraught family of the victim before issuing its verdict on Tuesday.
“The board has considered the totality of the information presented in this case and thoroughly deliberated on it, after which the decision was to deny clemency,” said a written statement. It did not disclose the vote breakdown.
Barring an unexpected turn of events, Davis will be put to death by lethal injection at 7:00 pm Wednesday local time (9am Thursday AEST) at a prison in Jackson, south of Atlanta, with the victim’s widow and — now grown-up — children looking on.
“We’ve been here three times before,” said Anneliese MacPhail, the mother of the slain police officer.
“We are ready to close this book and start our lives. This has been a long haul.”
Mr MacPhail’s daughter Madison, now 23, choked back the tears after the latest parole board hearing as she insisted the execution must go ahead because she had been robbed of a life with her father.
“I believe the death penalty is the correct source of justice,” she said.
All avenues for Davis now appear exhausted as Georgia’s governor does not have the power to stay executions and experts said any last-minute filings to the state courts or the US Supreme Court would likely prove unsuccessful.
“I am utterly shocked and disappointed at the failure of our justice system at all levels to correct a miscarriage of justice,” Davis attorney Brian Kammer said, as rights groups and activists rushed to condemn the decision.
Amnesty International called a protest rally for at the Georgia state capitol, exactly 24 hours before Davis is due to become the 34th person executed in the United States this year.
African American leaders condemned the parole board’s decision as emblematic of a US criminal justice system riven with racial inequality.
“This is Jim Crow in a new era,” declared Reverend Raphael Warnock of the Ebenezer Baptist Church, referring to American segregation laws overruled by the 1964 Civil Rights Act.
The American Civil Liberties Union urged Georgia’s prison workers to strike in a desperate bid to deprive the state of the wherewithal to carry out the execution.
At a protest outside Monday’s hearing, an estimated 150 to 200 demonstrators carried signs saying, “Justice, Free Troy Davis,” and “We are Troy Davis.”
Another placard read: “Too much Doubt. Save Troy Davis.”
Richard Dieter, executive director of the Death Penalty Information Center, said there was next-to-no chance Davis could earn a reprieve in what he called the “biggest capital punishment case in at least a decade.”
“I’m sure his lawyers will try to file something but I think even they are saying there is not much left that they have,” he said.
“Unless there is something nobody has heard about, it is unlikely there will be any relief.”
The US Supreme Court became involved in the Troy Davis case in 2009 and ordered a federal judge in Savannah to convene a hearing to consider new evidence.
In August 2010, however, a US District Court in Georgia ruled that Davis had failed to prove his innocence and denied him a new trial. The top US court turned down a subsequent appeal.
Davis supporters say close to one million people worldwide have signed petitions calling for clemency, with petitions last week delivered to state authorities containing about 650,000 signatures.
Some 300 rallies, vigils and events have been held worldwide, including in New York, Washington, Peru, Paris and Oslo.
Thirty-four of the 50 US states still have the death penalty and the Death Penalty Information Center says that since 1973 over 130 people have been released from death row with evidence of their innocence.