It then considered possible obstacles and rejected each in turn.
Among them was an executive order that bans assassinations. That order, the lawyers found, blocked unlawful killings of political leaders outside of war, but not the killing of a lawful target in an armed conflict.
A federal statute that prohibits Americans from murdering other Americans abroad, the lawyers wrote, did not apply either, because it is not “murder” to kill a wartime enemy in compliance with the laws of war.
But that raised another pressing question: would it comply with the laws of war if the drone operator who fired the missile was a Central Intelligence Agency official, who, unlike a soldier, wore no uniform? The memorandum concluded that such a case would not be a war crime, although the operator might be in theoretical jeopardy of being prosecuted in a Yemeni court for violating Yemen’s domestic laws against murder, a highly unlikely possibility.
Then there was the Bill of Rights: the Fourth Amendment’s guarantee that a “person” cannot be seized by the government unreasonably, and the Fifth Amendment’s guarantee that the government may not deprive a person of life “without due process of law.”
The memo concluded that what was reasonable, and the process that was due, was different for Mr. Awlaki than for an ordinary criminal. It cited court cases allowing American citizens who had joined an enemy’s forces to be detained or prosecuted in a military court just like noncitizen enemies.