Seems a bit odd that this was released as a blog post, but in any event, DoS Legal Adviser Harold Hongju Koh affirmed his March 25, 2010 ASIL speech; and went on specifically (reparagraphed to point up Mr Koh's five points):

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.
This is really OK - and Mr Koh's knees did not wobble - in his exclusive reliance on the Laws of War.

Regards

Mike