NEW YORK --The American Civil Liberties Union filed a lawsuit Thursday claiming the Bureau of Prisons has wrongfully withheld documents related toa secret CIA prison in Afghanistan known interchangeably by its nickname, "The Salt Pit," and its code name, "COBALT."

The Bureau of Prisons last year rejected an ACLU Freedom of Information Act request for documents about an inspection of the detention site conducted in November 2002. The visit to the site, which one CIA official called "the closest thing he has seen to a dungeon," was documented in a Senate Intelligence Committee report on torture, interrogation and detention, which was released in 2014.

The report describes the prison officials' visit to COBALT, where they saw detainees who stood for days naked and shackled to walls in total darkness, while loud music played nearly constantly, given only buckets for their waste. The prison officials were invited to inspect the site because CIA agents worried conditions were too harsh for them to elicit reliable intelligence from the detainees. Some of the detainees "'literally looked like (dogs) that had been kenneled.' When the doors to their cells were opened, 'they cowered,'" one interrogator said.

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Toward the end of the prison officials' visit, one detainee, Gul Rahman, died from apparent hypothermia, "naked except for a sweatshirt," according to the ACLU lawsuit, which was filed in the U.S. District Court in Washington.

Prison officials said they were "wow'ed" and had "never been in a facility where individuals are so sensory deprived," according to the Senate report. Still, they determined the site was sanitary, that detainees were not mistreated, and ultimately the site was not inhumane. They did however offer advice to improve safety for CIA officers.

Despite the Senate Report, in April 2015 the Bureau of Prisons responded to an ACLU request by writing that it had no files related to the COBALT visit. The ACLU's appeal of that response was rejected in September 2015.

Carl Takei, the attorney who filed the request, said it seems implausible that a domestic prison agency would send personnel to a war zone to inspect a detention site, and provide recommendations, but keep absolutely no record of the excursion.

"If it's clear that they do not have any documents in their possession, then the question becomes what happened to those documents. Were they destroyed? Did something else happened to them?" Takei asked in an interview with CBS News.

"I've never come across a situation where the Bureau of Prisons has had an ability to withhold documents that are not related to long-term law enforcement," Takei said.

He argued the case "raises serious questions" about the judgement of the prison officials who visited COBALT.

"Their responsibility with regards to COBALT was to examine the conditions and determine if they were humane --- the fact that it had people shackled to walls in the dark, in the cold, for days at a time, with only buckets for waste violates all human rights," Takei said. "They should never have rubber-stamped a torture chamber."

The Bureau of Prisons said in its April 2015 rejection of Takei's request that "no records were found" in its search for documentation of the COBALT visit.

If any records do exist, there is a process by which they could be kept secret, even though the Bureau of Prisons doesn't have the authority to classify documents, according to John Rizzo, who was the Acting General Counsel of the CIA -- the agency's top lawyer -- for more than half a decade.

Rizzo said in an interview with CBS News that when a non-intelligence office does work in support of an intelligence agency, they can essentially agree at the outset that the intelligence agency will take ownership of all material related to the work.

In other words: when the CIA asks prison officials to visit a secret interrogation site, it can stamp itself as the "originating agency" on any documents related to that visit, keeping and classifying those files as if the CIA produced them itself.

To University of Texas at El Paso law professor Bill Weaver, who served as a U.S. Army intelligence officer for eight years, that's a reasonable explanation.

"Agencies will work with each other on a magnificently uncontrolled basis when it's in both their interests," Weaver said. "You get very adept at making sure nobody can ever get at anything."

"I used to do it. If you ever have doubt about anything, you just start putting stamps on everything," Weaver said.

But even if the COBALT visit was originally a secret, at least some of the information sought by the ACLU should now be publicly available, according to Rizzo, who noted that officials spent years vetting the Senate report and removing classified information.

"Whatever was left in that report, the intelligence community determined was unclassified or declassified," Rizzo said.

And Takei said that an agreement between the Bureau of Prisons and the CIA allowing the intelligence agency to keep documents related to COBALT "wouldn't justify the bureau's response that it has no records whatsoever."

"At a minimum, one would expect that there would be records of internal approvals, travel, and the agreement itself, not to mention records of scheduling and other logistics for the meeting at the CIA back in Washington about the visit to COBALT," Takei said.

In June, Bureau of Prisons spokesperson Ed Ross declined to either confirm or deny that the visit detailed by the Senate Intelligence Committee even happened. The agency declined again on Wednesday to comment on all questions related to the report, instead referring CBS News to its Freedom of Information Act Service Center.

"We will not be providing any information regarding your inquiry," Ross said in June.