A MEMO ABOUT HOW the George W. Bush administration interpreted a ban on assassination can be kept secret, along with other legal documents about the drone war, a federal appeals court said in a ruling made public Monday.

For several years, the American Civil Liberties Union and the New York Times have been suing to wrench documents from the Justice Department’s Office of Legal Counsel that outline the rationale for killing suspected terrorists. Specifically, they sought the release of the justification for drone strikes that killed three U.S. citizens in Yemen in the fall of 2011: Anwar al Awlaki, his 16-year-old son, Abdulrahman al Awlaki, and Samir Khan.

Last year, the U.S. Court of Appeals for the Second Circuit in New York said that widespread discussion about the drone program by administration officials, as well as the leak of a so-called white paper from the Justice Department, outlining its legal reasoning for killing a U.S. citizen, had rendered moot the case for so much secrecy. The court ordered the government to release a July 2010 memo that cleared the way for killing Anwar al Awlaki. Two other documents discussing the CIA’s role in such killings were also made public last year, in heavily redacted form.

Today’s decision from the court centered on 10 remaining documents that the Justice Department argued did not have to be released.

One of the documents at issue was a March 2002 memo, which, in the government’s description, “provided legal advice regarding the assassination ban in Executive Order 12333.” (The order, signed by Ronald Reagan in 1981, upholds a ban on assassination first issued by Gerald Ford in 1976.)

The memo might get at the heart of a debate about the United States’ lethal counterterrorism missions, carried out by drone or other means: Why is the killing of select individuals, far from conventional battlefields, without a trial, not assassination?

The Obama administration prefers the terms “targeted killing” or “high-value targeting,” to describe these strikes (with many journalists following suit). The word assassination implies that the killings are illegal, and the government argues, of course, that they are legal, under the laws of war or of self-defense. But the ban on assassination is brief and contains no definition of the word itself. And for the most part, every administration’s interpretation of it has been done in secret. The details of the Obama administration’s arguments, in the drone memos that have been released, are redacted.

For the time being, it will stay that way. In ruling Monday against the disclosure of the 2002 memo, the appeals judges said that it long predates public commentary about the drone war by Obama administration officials, and “the context in which the official spoke might be significantly different from the context in which the earlier document was prepared.”

Jameel Jaffer, deputy legal director of the ACLU, was disappointed with the court’s decision and urged the Obama administration to release more information about the drone program of its own initiative.

“In a democracy, there should be no room for ‘secret law,’ and the courts should not play a role in perpetuating it,” Jaffer said in a statement. “The government should not be using lethal force based on standards that are explained only vaguely and on facts that are never published or independently reviewed.”

More than 13 years after the United States’ first drone strike in Yemen in 2002, few primary source materials about the drone war have been made public. Secret military documents published by The Intercept last month showed the expansion of the drone war under the Obama administration and underlined the degree to which the administration’s public portrait of its drone strikes — as a limited, precision effort against individuals who posed an imminent threat to the United States – did not always match the reality of the campaigns.

Top photo: Tribesmen stand on the rubble of a building destroyed by a U.S. drone strike in Azan, Yemen. Sixteen-year-old Abdulrahman al Awlaki, an American citizen and son of slain U.S.-born cleric Anwar al Awlaki, was killed in a drone strike on this building in 2011, along with six suspected al Qaeda militants. Anonymous U.S. officials have raised questions over whether Abdulrahman al Awlaki was deliberately targeted.