Troy Davis' offer to take a polygraph test to stave off his execution today by lethal injection has been rejected by Georgia authorities who plan to carry out the sentence.
Davis, who is scheduled to die by lethal injection at 7 p.m. today, was denied clemency by the state's Board of Pardons and Paroles on Tuesday.
A spokeswoman for Amnesty said Davis' request was "a bit of a risky strategy" because polygraph evidence is unreliable. In the Green River serial killer case, for example, Gary Ridgway passed a polygraph in 1984, and only confessed to the murders 20 years later when presented with DNA evidence.
Davis was convicted in the 1989 shooting death of Savannah police officer Mark Allen MacPhail, while he worked an off-duty security job.
Related: Parole Board Denies Clemency for Ga. Cop Killer