There is a second torture report locked away somewhere at CIA headquarters in Langley, Virginia. The agency says the document is so sensitive that national security would be at risk if any details about it were publicly revealed.

But last week, outgoing Senator Mark Udall of Colorado, in his final speech on the Senate floor and in the wake of the release of the Senate Intelligence Committee's executive summary of the so called torture report, discussed the document at length. Udall called the still-secret CIA report - dubbed the Panetta Review after former CIA Director Leon Panetta - a "smoking gun."

This is the document that has been at the center of the war of words between the Senate Intelligence Committee and the CIA; virtually everything about it has been shrouded in secrecy. VICE News filed a Freedom of Information Act (FOIA) lawsuit against the CIA seeking access to the Panetta Review, and last week, a CIA lawyer named Martha Lutz provided us with a declaration explaining why we can't have it. However, she disclosed new details that finally shed light on what the Panetta Review is.

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Udall, a member of the Senate Intelligence Committee, first disclosed the existence of the Panetta Review a year ago at a confirmation hearing the committee held for Caroline Krass, the CIA's top lawyer. At the time, the committee and the CIA were battling over the conclusions the committee reached in a classified report into the agency's detention and interrogation program. The committee completed its study in December 2012 and then voted to declassify and publicly release an executive summary.

The CIA drafted a rebuttal to the Senate's 6,700-page report in June 2013. The agency said in its response that the Intelligence Committee's finding that the "enhanced interrogation" techniques high-value CIA captives were subjected to at black site prisons failed to produce "unique" and "valuable" intelligence was wrong.

CIA Director John Brennan attempted to block the Senate from releasing a declassified executive summary of its report, which set off a yearlong fight between the agency and the committee that nearly boiled over into a constitutional crisis.

That's why Udall revealed details about the Panetta Review during Krass's confirmation hearing. He said the agency's official response to the Senate's 5-year-long study of the program contradicted what the Panetta Review said about the program. In fact, Udall said the Panetta Review reached the same conclusions as the Senate Intelligence Committee - notably that the CIA lied to Congress, the White House, and the public about the efficacy of enhanced interrogation techniques, and that the methods were far more brutal than the CIA had let on.

"It appears that [the CIA's internal detention and interrogation program review], which was initiated by former Director Panetta, is consistent with the Intelligence Committee's report, but amazingly it conflicts with the official CIA response," Udall said. "If this is true, it raises fundamental questions about why a review the CIA conducted internally years ago... is so different from the CIA's formal written response to the committee study."

In a dramatic 45-minute floor speech last March devoted entirely to the Panetta Review, Senate Intelligence Committee chairwoman Dianne Feinstein described how the committee gained access to it in late 2010 (the CIA first learned that the committee obtained the Panetta Review when Udall referred to it during the confirmation hearing). She said committee staffers discovered it using the "search tool" provided to the committee by the CIA to scour more than 6 million pages of highly classified records about the program that the CIA made available.

"We have no way to determine who made the Internal Panetta Review documents available to the committee," Feinstein said. "Further, we don't know whether the documents were provided intentionally by the CIA, unintentionally by the CIA, or intentionally by a whistle-blower."

Feinstein shed a little more light on what the Panetta Review is but her description was vague. In her floor speech she said, "We believe these documents were written by CIA personnel to summarize and analyze the materials that had been provided to the committee for its review" of the CIA's detention and interrogation program. "The Panetta review documents... appeared to be based on the same information already provided to the committee... and acknowledgement of significant CIA wrongdoing."

Feinstein also leveled explosive allegations against the CIA during that speech, accusing the agency of spying on the committee during its investigation of the program by monitoring its computers at a secure facility in Northern Virginia:

I have grave concerns that the CIA's search may well have violated the separation of powers principles embodied in the United States Constitution, including the Speech and Debate clause. It may have undermined the constitutional framework essential to effective congressional oversight of intelligence activities or any other government function. Besides the constitutional implications, the CIA's search may also have violated the Fourth Amendment, the Computer Fraud and Abuse Act, as well as Executive Order 12333, which prohibits the CIA from conducting domestic searches or surveillance.

The CIA, meanwhile, accused committee staffers of illegally accessing the Panetta Review by hacking into the CIA's network. In a letter sent to Feinstein last January, Brennan said the Panetta Review is "sensitive, pre-decisional CIA material" and the committee was not allowed to see it. The CIA demanded that the Panetta Review be returned. The committee, which placed a copy of the Panetta Review in a safe at its offices in the Hart building on Capitol Hill, refused.

"The Executive branch has long had substantial separation of powers concerns about congressional access to this kind of material," Brennan said.

He told Feinstein that in late 2013 he authorized CIA personnel to conduct a search of the committee investigators' computers at the secure facility to determine how they obtained the Panetta Review after a review of computer "audit logs" concluded CIA did not turn it over. Feinstein said the search was conducted without her knowledge or approval.

"Because we were concerned that there may be a breach or vulnerability in the system for housing highly classified documents, CIA conducted a limited review to determine whether these files were located on the [Intelligence Committee] side of the CIA network and reviewed audit data to determine whether anyone had accessed the files, which would have been unauthorized," Brennan said.

A CIA lawyer filed a crimes report with the Department of Justice (DOJ) against the Senate. The CIA's internal watchdog referred the claims that agency personnel had spied on Senate staffers to DOJ to determine if any crimes were committed.

But the Justice Department declined to launch a criminal investigation on either matter. Last July, CIA inspector general David Buckley concluded that the CIA breached Senate staffers' computers and spied on them. Brennan issued an apology and commissioned an "Accountability Board at CIA," chaired by former Senator Evan Bayh, who used to be a member of the Intelligence Committee, to further look into the matter.

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Lutz, the CIA lawyer, explained in her declaration that the Panetta Review is "actually a series of more than forty draft documents relating to the CIA's former detention and interrogation program." She said the "top-secret" drafts, which were never given an official name, "were originally envisioned as providing summaries of documents being provided" to the Senate Intelligence Committee that Panetta and other CIA officials "could consult to figure out how to respond to the Senate's investigation into the CIA's torture program.

"The drafts were intended to inform CIA leaders' decision-making by highlighting the most noteworthy information contained in the millions of pages of documents being made available to the [Intelligence Committee] in connection with its study," Lutz said.

When the Senate Intelligence Committee announced in 2009 that it had launched an investigation into the CIA's detention and interrogation program, Panetta said that he, too, planned to review it. He announced the formation of a Director's Review Group for Rendition, Detention, and Interrogation, whose investigation would run parallel to the one being conducted by the Senate Intelligence Committee.

"Peter Clement, a senior leader from our Directorate of Intelligence, will head this new unit, which will have a small number of officers from across the agency, including the National Clandestine Service," Panetta said in a memo to CIA staff.

But that review group was disbanded and never completed its work. Senator Martin Heinrich of New Mexico attempted to get Brennan to discuss on the record during a congressional hearing last January why that was.

"I'll be happy to address that question at the time when the committee leadership requests that information from me," Brennan said.

Lutz's declaration provides details about what happened.

"A team of CIA employees and contractors worked on the drafts between mid-2009 and mid-2010 at which point work was suspended," she said. "The documents remain in draft form, were never completed, and were not presented as final products to [Panetta] or other senior CIA leaders."

Because the CIA had to search for and then turn over a high volume of classified material about its enhanced interrogation program to the Intelligence Committee, the agency wanted to keep Panetta and other senior CIA officials informed about the "significant information" and "significant issues" contained in those documents that the Senate committee was likely to focus on.

Two groups were tasked with the responsibility: the Director's Review Group and a Special Review Team, the latter made up of about 10 CIA employees and contractors focusing "exclusively" on reviewing the documents turned over to the Senate Intelligence Committee and "preparing summaries of certain key information in those documents.

"The leaders of the Special Review Team assigned each team member one or more research topics," Lutz said in her declaration. "Some topics focused on individual detainees and other topics focused on overarching programmatic subject matters.... When the team members identified information they believed was significant on a given topic, they described that information in their Draft Review. The intent, over time, was for each Draft Review to become a rough guide to noteworthy information on a particular topic."

For example, a Draft Review may contain details about the rectal feeding or rectal rehydration of detainees in custody of the agency, which the Senate Intelligence Committee's 525-page executive summary found was used on at least five detainees.

The Special Review Team worked on the Draft Reviews for about a year, then "ceased their efforts in 2010." That was about the time Intelligence Committee staffers gained access to the documents.

The review team abruptly ended its work, according to Lutz, because the CIA believed the review could interfere with a separate criminal probe conducted by a special prosecutor into the CIA's detention and interrogation program.

Lutz said the Draft Reviews, the documents the Senate refers to as the Panetta Review, were intended for CIA eyes only. In other words, Lutz is asserting that the Panetta Review is exempt from disclosure under the FOIA because it's a "deliberative" document, meaning it's part of a behind-the-scenes decision-making process.

She said a majority of the Draft Reviews are incomplete, "contain only rough notes," and cover less than half of the 6 million pages of CIA documents the Senate Intelligence Committee reviewed to draft its report. Because the special review group disbanded, CIA officials never had an opportunity to review its work.

The Panetta Review documents contain markings indicating they are still in draft form.

"Each document is stamped 'DELIBERATIVE PROCESS PRIVILEGED DOCUMENT' at the top of every page, and most of the documents are marked 'DRAFT' on every page as well. Each document also bears the following language at the top [of] the first page:

This classified document was prepared by the CIA Director's Review Group for Rendition, Detention and Interrogation (DRG-RDI) for DRG-RDI's internal discussion purposes and should not be used for any other purpose, nor may it be distributed without express permission from DRG-RDI or CIA's Office of General Counsel. This document contains [certain classified information]. This document also contains material protected by the attorney-client and attorney work product privileges. Furthermore, this document constitutes deliberative work product, protected by the deliberative-process privilege, and is not a final, conclusive, complete or comprehensive analysis of DRG-RDI, in support of informing senior Agency officials about broad policy issues. While every effort was made to ensure this document's accuracy, it may contain inadvertent errors. For this reason, and because this document selectively summarizes, draws inferences from, or omits information from the sources it cites, it should not be relied upon by persons outside DRG-RDI.

Those classification markings, according to a CIA official, are evidence that the Senate Intelligence Committee improperly accessed the documents and violated a security agreement it entered into with the agency in 2009. And that's what the Republican minority members of the Senate Intelligence Committee contend in their response to the Democrats' executive summary, which devotes an entire section to the document.

"Committee majority staff knowingly removed the Panetta Internal Review, a highly classified, privileged CIA document, from a CIA facility without authorization and in clear violation of the existing agreed-upon procedures by the Committee and the CIA," the Republican committee members wrote.

Tom Mentzer, a spokesman for Feinstein, pointed VICE News to comments the Intelligence Committee chairwoman made on the Senate floor about the claims that the documents were privileged and marked up by CIA to indicate they were not to be shared.

"We have discussed this with the Senate Legal Counsel who has confirmed that Congress does not recognize these claims of privilege when it comes to documents provided to Congress for our oversight duties," Feinstein said. "We believe we had every right to review and keep the documents."

Steven Aftergood, the director of the Project on Government Secrecy at the Federation of American Scientists, said Lutz's declaration is "fascinating" because it "sheds new light on the origins and the purpose of the so-called Panetta Review."

"It shows that just as the Senate Intelligence Committee was working to digest millions of pages of records and to reduce them to a coherent narrative, the CIA itself was doing pretty much the same thing," he said. "In effect, it was performing its own parallel assessment of this voluminous documentary material to help the Agency anticipate the Senate Committee's findings. So of course the resulting Review would be a valuable document (or set of documents) to obtain and to read."

But he did not interpret the declaration to say anything about the propriety of Senate access to this material.

"I think it is silent on that subject," he said. "The markings (e.g., "don't distribute") are directed at CIA personnel, not at the Senate staffers."

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So what will become of the Panetta Review? Although he's now officially out of office, Udall said he would continue to press for its release.

"... I think the truth had to come out, and the Panetta review needs to be declassified and released," Udall said in an interview with Politicolast week.

Only three pages of documents related to the Panetta Review have been released: emails that were turned over to Politico earlier this year. CIA Director Brennan said the Panetta Review will likely never see the light of day.

He was asked about it at a rare press briefing last week where he discussed the findings of the Senate Intelligence Committee's scathing report on the torture of detainees in custody of the CIA.

"As far as the so-called Panetta Review ... This was an internal document that was never completed and it's one that I believe is a(n) internal deliberative document and therefore something that was not subject to the committee's oversight," Brennan said. "In addition, it was outside of the scope of the period of time that was covered by the agreement that was worked between Senator Feinstein and Leon Panetta about the documents that would be provided to the committee. It was subsequent to that ... I think there's more than enough transparency that has happened over the last couple days. I think it's over the top."