State Department Legal Adviser Harold Koh, a harsh critic of the Bush administration's anti-terrorism policies and a leading expert in international law, took to the Opinio Juris blog to defend the legality of the killing of Osama bin Laden:
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. By enacting the AUMF, Congress expressly authorized the President to use military force “against … persons [such as bin Laden, whom the President] determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001 …in order to prevent any future acts of international terrorism against the United States by such … persons” (emphasis added). Moreover, the manner in which the U.S. operation was conducted—taking great pains both to distinguish between legitimate military objectives and civilians and to avoid excessive incidental injury to the latter—followed the principles of distinction and proportionality described above, and was designed specifically to preserve those principles, even if it meant putting U.S. forces in harm's way. Finally, consistent with the laws of armed conflict and U.S. military doctrine, the U.S. forces were prepared to capture bin Laden if he had surrendered in a way that they could safely accept. The laws of armed conflict require acceptance of a genuine offer of surrender that is clearly communicated by the surrendering party and received by the opposing force, under circumstances where it is feasible for the opposing force to accept that offer of surrender. But where that is not the case, those laws authorize use of lethal force against an enemy belligerent, under the circumstances presented here.
I think the question of proportionality in the bin Laden operation is one for which the administration hasn't gotten enough credit, although its motives--ensuring there was a body--may not have been entirely altrustic. But by opting for a raid rather than a drone strike, they likely preserved innocent lives that would have otherwise been lost. Whether a genuine offer of surrender would have been accepted is a separate question and one people are entitled to raise, but given the fact that the SEALs were dealing with the leader of a group whose primary weapon of destruction is suicide bombing it's hard for me to second-guess their decisionmaking. The possibility that bin Laden was prepared to kill everyone in the near vicinity in the event of being discovered was much higher than it might be with a different target.
Now you don't have to take Koh's word for it, but for reasons I've outlined before I think bin Laden was a lawful military target. There isn't much of the way of precedent in international or domestic law that says otherwise--the laws of war exist to reduce suffering for noncombatants, protect prisoners of war, and ensure proportionate uses of force. But one thing they don't do is prevent declared combatants from killing each other.
UPDATE: Just so we're clear, I'm not arguing that it would have been legal to kill bin Laden if he had surrendered or been captured. As I've said before, that would be a war crime. What I'm saying is that the SEALs weren't under any obligation to offer him an opportunity to surrender beforehand.
