The Central Intelligence Agency is under renewed legal pressure to release “thousands” of records pertaining to its international drone war, following an appeal filed Monday by the American Civil Liberties in Washington, D.C. The motion comes just days after The Intercept published an eight-part series based on cache of secret documents detailing the U.S. military’s parallel reliance on unmanned airstrikes in the war on terror.

While The Intercept’s series, The Drone Papers, offered new insights into the Pentagon’s drone missions in Yemen, Somalia, and Afghanistan, the CIA’s covert drone war has largely remained an official black hole. In the absence of verifiable facts and documentary evidence regarding the agency’s operations, the task of mapping and understanding a central component of modern American warfare has fallen on journalists and legal organizations.

The ACLU’s Monday filing marks the latest chapter in one such effort — a five-year legal battle with the U.S. government over the CIA’s program that began with a 2010 freedom of information request calling for a release of official documents detailing when, where, and against whom the U.S. considers itself authorized to conduct drone strikes, as well as information illustrating how the attacks are consistent with international law.

Following the request, the CIA initially refused to confirm whether its drone program existed. The ACLU challenged that defense, noting that numerous U.S. officials had publicly confirmed its existence. In March 2013, a lower court ruling siding with the CIA was reversed by a unanimous 3-0 decision in favor of the ACLU.

In the wake of the reversal, the ACLU narrowed its FOIA request to two criteria: first, any and all legal memoranda “concerning the U.S. Government’s use of armed drones to carry out premeditated killings”; and, second, “records containing charts or compilations about U.S. Government strikes sufficient to show the identity of the intended targets, assessed number of people killed, dates, status of those killed, agencies involved, the location of each strike, and the identities of those killed if known.”

Responding to the narrowed requests, the CIA revealed that it had located a dozen final legal memoranda (one of which the government made public in redacted form), and “thousands of classified intelligence products responsive” to the ACLU’s second request. The agency has maintained that the documents are exempt from FOIA publication requirements. At issue now, as the ACLU’s recent filing lays out, is the question of whether the information will be released.

“This case concerns the CIA’s withholding of records that would allow the public to better understand and evaluate the effectiveness, lawfulness, and morality of the government’s drone campaign,” the ACLU noted in its brief. “The CIA continues to withhold essentially everything, and public debate about the drone campaign continues to be impoverished and distorted by unwarranted secrecy and selective disclosure. FOIA was enacted to prevent precisely this.”

Jameel Jaffer, deputy legal director of the ACLU, told The Intercept that the current appeal rests on two arguments. The first, that legal analysis cannot be classified in and of itself, and that it can only be withheld insofar as it is bound up with appropriately classified facts. The ACLU contends that the government has not proven that the facts underlying the legal memoranda are classified. The second argument is that the strike data sought is not, as the CIA contends, exempt from FOIA on the grounds of sources and methods. The CIA declined to comment on the appeal.

The information sought by the ACLU pertains to an ongoing debate over the nature of the CIA’s role in combatting terrorism. During his February 2013 nomination hearing, John Brennan was asked to reflect on a question that has loomed over the spy agency since the September 11 attacks: Has the CIA become overly militarized? Barbara Mikulski, the Maryland senator who posed the question, described the agency’s increased role in paramilitary operations as “mission creep.”

After noting that the CIA’s core mission is intelligence collection, Brennan conceded that “there are things that the agency has been involved in since 9/11 that, in fact, have been a bit of an aberration from its traditional role.” Brennan said that if confirmed he would “take a look at that allocation of mission within CIA,” adding that “the CIA should not be doing traditional military activities and operations.”

The “aberration[s]” and “things that the agency has been involved in since 9/11,” are numerous, but in raising the issue of “traditional military activities and operations” Brennan seemed to be making a veiled reference to the CIA’s drone war, which, according to figures compiled by the Bureau of Investigative Journalism, has included more than 400 strikes in Pakistan alone, resulting in 423 to 965 civilian deaths.

Despite Brennan’s hints of a return to a more restrained mission, the CIA in the age of Obama continues to be an actively lethal organization. Following the unintended killing in January of two Western hostages in a CIA drone strike, the Wall Street Journal revealed that while the president had publicly declared a tightening of guidelines surrounding drone strikes in May 2013, “he secretly approved a waiver giving the Central Intelligence Agency more flexibility in Pakistan than anywhere else to strike suspected militants.”

While the CIA’s drone war has sparked outrage from human rights organizations across the world, it has enjoyed consistent support on Capitol Hill, where congressional staffers routinely watch videos of the agency’s airstrikes and receive assurances from influential CIA officials that the operations are necessary and efficient.

Jaffer argues that in refusing to release key details regarding the legality and efficacy of its counterterrorism operations, the U.S. government increases the potential for information to be revealed by whistleblowers.

“Government officials frequently complain of whistleblowers’ purported failure to use ‘official channels’ for disclosure,” Jaffer wrote in a post for the website Just Security Monday night. “But perhaps the complaint would be marginally more sympathetic if the government were complying with the FOIA. Whistleblowers would surely be less inclined to disclose information through unofficial channels if the government were complying with its legal obligation to disclose information through official ones.”

Read the complete Drone Papers.