The US state of Georgia is preparing to execute death row inmate Troy Davis by lethal injection, despite pleas from supporters to overturn his conviction.
Seven witnesses have recanted their testimony in the case, and protests and vigils are planned throughout the day.
Davis' lawyers say prison officials have blocked a polygraph test for Davis, who maintains he is innocent.
He was convicted in 1991 of killing Mark MacPhail, an off-duty police officer.
The Georgia Board of Pardons and Paroles has rejected an appeal to reconsider their Monday decision to deny Davis clemency.
Prosecutors say they have no doubts as to his guilt.
Spencer Lawton, the district attorney who secured the conviction, told the Associated Press news agency he was embarrassed the execution had taken so long.
"What we have had is a manufactured appearance of doubt which has taken on the quality of legitimate doubt itself. And all of it is exquisitely unfair," he said.
On Wednesday morning, Davis' lawyers filed a last-ditch appeal to the county court responsible for Georgia's death row, arguing that ballistic testing from the case was flawed.
Protests in Georgia have been organized by the Amnesty International and NAACP The 42-year-old's conviction has been upheld by several federal and appeal courts.
He was denied a hearing at the US Supreme Court after a federal judge refused a new trial for his case.
Davis' execution date has been rescheduled four times.
International protestsWhile vigils have been scheduled at both the Georgia state capitol and the jail, protests have taken on an international dimension since Monday's decision to deny clemency.
The Council of Europe has called for Davis' sentence to be commuted.
Renate Wohlwend of the Council's Parliamentary Assembly said: "To carry out this irrevocable act now would be a terrible mistake which could lead to a tragic injustice."
Amnesty International and other groups have planned protests at the US embassies in Paris and London.
Davis also counts as supporters Pope Benedict XVI and former US President Jimmy Carter, as well as US conservative figures like representative Bob Barr and former FBI Director William Sessions.
