According to officials familiar with the deliberations, the lawyers threw themselves into the project and swiftly completed a short memorandum. It preliminarily concluded, based on the evidence available at the time, that Mr. Awlaki was a lawful target because he was participating in the war with Al Qaeda and also because he was a specific threat to the country. The overlapping reasoning justified a strike either by the Pentagon, which generally operated within the Congressional authorization to use military force against Al Qaeda, or by the C.I.A., a civilian agency which generally operated within a “national self-defense” framework deriving from a president’s security powers.
They also analyzed other bodies of law to see whether they would render a strike impermissible, concluding that they did not. For example, the Yemeni government had granted permission for airstrikes on its soil as long as the United States did not acknowledge its role, so such strikes would not violate Yemeni sovereignty.