A defense attorney says Georgia prison officials have blocked inmate Troy Davis from taking a polygraph test before his scheduled execution.

Attorney Stephen Marsh told The Associated Press on Wednesday that the Georgia Department of Corrections has denied his request to allow Davis to take a polygraph test. Davis is scheduled to die at 7 p.m. EDT Wednesday.

Davis 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 MacPhail's relatives say they have no doubt the right man is being punished.

Marsh had said he hoped the polygraph test would convince the state pardons board to reconsider a decision against clemency.

Tags: Georgia, death penalty, Troy Davis, execution, polygraph test