Harold Koh: 'The Lawfulness of the U.S. Operation Against Osama bin Laden'

At Opinio Juris (via Glenn Reynolds and Memeorandum):

Given bin Laden’s unquestioned leadership position within al Qaeda and his clear continuing operational role, there can be no question that he was the leader of an enemy force and a legitimate target in our armed conflict with al Qaeda. In addition, bin Laden continued to pose an imminent threat to the United States that engaged our right to use force, a threat that materials seized during the raid have only further documented. Under these circumstances, there is no question that he presented a lawful target for the use of lethal force.