A federal court on Monday released a previously secret government memo outlining the legal justification for the 2011 killing of Anwar al-Awlaki, a U.S. citizen and accused al-Qaeda operative, in a drone strike in Yemen.

The document was released under order of the U.S. Court of Appeals for the 2nd Circuit in New York and provides the most detailed explanation to date for the legal reasoning behind Awlaki’s killing. Its disclosure also represents a significant capitulation by the Obama administration, which fought for years to keep the memo — as well as many other aspects of its targeted-killing program — secret from the public.

“We do not believe that al-Aulaqi’s U.S. citizenship imposes constitutional limitations that would preclude the contemplated lethal action” by the U.S. military or CIA, the memo concluded, clearing the way for a drone strike that would trigger intense legal and political debate.

Civil liberties groups welcomed the disclosure of the 41-page memo.

“The release of this memo represents an overdue but nonetheless crucial step towards transparency,” said Jameel Jaffer, the deputy legal director of the American Civil Liberties Union, which along with the New York Times had filed Freedom of Information Act lawsuits to compel the government to release the July 2010 document.

This October 2008 photo shows Imam Anwar al-Awlaki in Yemen. (Anonymous/Via AP)

“The release of this memo will allow the public to better understand the scope and implications of the authority the government is claiming,” Jaffer said.

Important sections of the Justice Department’s legal analysis were stripped from the version of the document released to the public. Among the deleted portions were paragraphs that presumably explained why the Justice Department’s Office of Legal Counsel determined that killing Awlaki in a drone strike would not violate the Fourth Amendment, which guarantees due process to U.S. citizens accused of crimes.

Still, the memo provides previously unknown details about the reasoning behind one of the most controversial counterterrorism operations carried out by the U.S. government since the Sept. 11, 2001, attacks.

Awlaki’s relationship with al-Qaeda “brings him within the scope” of the 2001 congressional authorization of the use of military force, according to the document. Citing information provided by the CIA and Pentagon, the memo said Awlaki has “operational and leadership roles” with al-Qaeda and “continues to plot attacks intended to kill Americans.”

In part because that authorization specified no geographic boundaries, it did not matter that Awlaki was based in Yemen rather than Afghanistan, where the bulk of the U.S. war effort against al-Qaeda was focused.

The memo explores a range of other potential legal issues, finding, for example, that federal laws designed to prevent U.S. nationals from getting away with murder overseas “had nothing to do with the conduct of an authorized military operation by U.S. armed forces.”

The document makes no specific mention of armed U.S. drone aircraft, referring only to “contemplated lethal operations.” But the memo was drafted at a time when drone attacks and other U.S. airstrikes had begun to surge in Yemen, from two in 2009 to 41 in 2012, according to the Long War Journal Web site.

Even before the Justice Department memo was signed, Awlaki had been added to U.S. “kill lists.”

A Muslim cleric born in New Mexico, Awlaki was killed in a CIA drone attack in September 2011, after being linked to an al-Qaeda affiliate in Yemen that had mounted a series of terrorist plots against the United States. Among them was the attempted bombing of a Detroit-bound airliner on Christmas Day in 2009.

The administration has acknowledged killing three other U.S. citizens in Yemen, including Awlaki’s teenage son in a separate strike a month after his father was killed. But only the elder Awlaki was targeted intentionally, according to U.S. officials who have said the others were killed incidentally in strikes against other targets.

The memo includes a section devoted specifically to the legality of lethal operations carried out by the CIA, marking a rare instance in which the agency’s role in the drone program has been so formally acknowledged.

The broad outlines of the memo have been disclosed previously, including in a letter that Attorney General Eric H. Holder Jr. sent to the Senate Judiciary Committee saying that targeting a U.S. citizen was seen as a last resort but permissible as long as the person posed “an imminent threat of violent attack against the United States” and that capture was “not feasible.”

The newly released document indicates that both the U.S. military and the CIA had assured the Justice Department that “they intend to capture” Awlaki but had made clear that doing so “would be infeasible at this time.”

While acknowledging that killing a U.S. citizen carries “the risk of erroneous deprivation of a citizen’s liberty in the absence of sufficient process,” the memo argued that those considerations are overwhelmed when the target poses “a continued and imminent threat of violence or death” to other Americans.

The memo was signed by David J. Barron, who later left the Office of Legal Counsel to return to his position at Harvard Law School. Barron has since been confirmed to a position on a federal appeals court. Members of Congress threatened to block his nomination unless the Awlaki memo was released.

Sen. Ron Wyden (D-Ore.), a member of the Senate Intelligence Committee, said in a statement that he hoped that the release of the memo would “generate new pressure for the executive branch to answer other pressing questions,” including whether the president can order an American killed “anywhere in the world” and what it means “to say that capturing an American must be ‘infeasible.’ ”