On Monday morning a United States federal appeals court released the secret Obama administration memo that provided legal justification for the 2011 drone strike in Yemen that killed U.S. citizen Anwar al-Awlaki, an alleged al Qaeda leader.

Reuters explains the rationale, as put forth by the document:
The memo, prepared by the Justice Department's Office of Legal Counsel, says that because the U.S. government considered al Awlaki to be an "operational leader" of an "enemy force," it would be legal for the CIA to attack him with a drone "as part of the United States' ongoing non-international armed conflict with al Qaeda," even though he was a U.S. citizen.

The memo also says the killing of al Awlaki by U.S. military forces would be legal under an authorization for the use of U.S. military force approved by Congress following the Sept. 11, 2001, attacks on New York and Washington, D.C.
While capturing al Awlaki would have been preferable, the memo states that "we also understand that an operation by either agency to capture al-Aulaqi in Yemen would be infeasible at this time."

View the full document below, with the drone memo starting on page 67: