The US Supreme Court has rejected an appeal for a stay of execution from lawyers for the man behind the 2002 sniper attacks in Washington DC.
John Allen Muhammad is due to be executed by lethal injection on Tuesday for the murder of Dean Harold Meyers, one of 10 people killed during three weeks of attacks.
His lawyers say Muhammad is mentally ill.
The BBC reports the court gave no reason for the rejection of the clemency appeal.
Muhammad has one final appeal for clemency pending before the Virginia Governor.
Muhammad's then teenage accomplice, Lee Boyd Malvo, is serving life in prison for his part in the attacks.
The two men killed six people in Alabama and Louisiana before moving on to Maryland, Washington and Virginia.