WASHINGTON, Oct 6, 2008 (AFP) - The US Supreme Court refused Monday to hear arguments in the case of an African-American granted an 11th hour stay of execution for the murder of a white police officer.

The execution of Troy Davis, 39, who has spent 17 years on death row in Georgia, was dramatically halted two hours before he was due to die late last month amid doubts about his conviction.

Defense lawyers had asked the Supreme Court to rule on the constitutionality of executing a person when there is new, substantial evidence to show he was not guilty of the crime.

Seven out of nine witnesses who gave evidence at Davis' trial have recanted or changed their testimony that he murdered policeman, Mark MacPhail.

The witnesses said statements implicating Davis had been coerced by strongarm police tactics, challenging the backbone of the prosecution's case in the absence of any weapon, fingerprints and DNA linking him to the murder.