A trial was under way on Wednesday in the western German city of Duesseldorf against a suspected Islamic State terrorist.
The federal prosecution charged the 25-year-old from Dinslaken in the Lower Rhine region with being a member of an Islamic State special unit.
As a storm trooper the man is supposed to have used violence against spies and deserters from the terrorist group and returned them to Islamic State prisons.
The defendant had previously acted as a witness in two terrorist cases, where he confirmed his service in the special unit. He admitted to witnessing torture and execution, but denies any involvement in the acts.