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The harsh interrogation techniques used by the CIA in the years after Sept. 11 were essentially useless and far more brutal than the spy agency told Congress and the public, according to a long-awaited Senate report released Tuesday.

It found that CIA interrogation tactics, employed for days or weeks at a time, never led to "imminent threat" intelligence — the figurative ticking time bomb often cited as justification. In some cases, the means were counterproductive, the report found.

Among the techniques described were waterboarding so severe it produced convulsions, sleep deprivation so prolonged it induced hallucinations, the slamming of detainees into walls, the denial of medical care and unnecessary rectal feeding.

One prisoner, Khalid Sheikh Mohammed, the alleged architect of the Sept. 11 attacks, was waterboarded 183 times in what was described as "a series of near-drownings."

"It is my personal conclusion that, under any common meaning of the term, CIA detainees were tortured," Sen. Dianne Feinstein, D-California, chairwoman of the Senate Select Committee on Intelligence, said in an introduction to the report.

Read the Senate Intelligence Committee report (PDF)

On the Senate floor, she acknowledged concerns that releasing the report could provoke blowback overseas and endanger U.S. military and diplomatic installations. And she stressed that she was not condemning the CIA as a whole.

But she said: "History will judge us by our commitment to a just society governed by law and the willingness to face an ugly truth and say: Never again."

Gruesome details

The report examined the CIA's secret overseas detention of at least 119 people during the administration of President George W. Bush. It criticized the CIA for "inadequate and deeply flawed" management of the interrogation program, including improper screening and poor training of interrogators.

According to a summary provided to reporters, the most aggressive techniques were used "in combination and nonstop," including keeping detainees awake for as long as 180 hours, standing or in stress positions.

In just one example, the report quoted internal CIA documents describing the prolonged interrogation of one detainee, Abu Zubaydah, as so intense that several members of the CIA's own team were affected "to the point of tears and choking up."

Side by side, the report showed congressional testimony by Michael Hayden, the former CIA director, in which he denied that CIA personnel expressed any reservations about interrogation techniques.

During at least one waterboarding session, the report said, Zubaydah "became completely unresponsive, with bubbles rising through his open full mouth." After medical help, he regained consciousness and expelled "copious amounts of liquid."

At one secret CIA site, detainees were subjected to what was known as a rough takedown: CIA officers would scream at a detainee, drag him out of his cell, cut off his clothes, bind him with tape, put a hood over his face and drag him down a corridor while slapping and punching him.

Another detainee was threatened with the sexual abuse of his own mother, the report said.

Few results

According to the Senate report, the CIA's own records found that seven of 39 detainees subjected to especially aggressive interrogation yielded no intelligence, and that others provided useful information without being subjected to the harsh techniques.

Other detainees who were harshly interrogated made up information, including about "the terrorist threats which the CIA identified as its highest priorities," the report found.

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The Senate committee said that it had reviewed 20 of the most commonly cited examples of successes attributed by the CIA to enhanced interrogation. It found each of those examples wrong.

Of 119 known detainees in CIA custody during its program of harsh interrogation, at least 26 were wrongly held, the committee found.

The CIA hired two psychologists to help devise and carry out the interrogation techniques, the report found. Neither had experience as an interrogator, expertise in counterterrorism or specialized knowledge of al Qaeda, the report said. They were paid $80 million.

Misleading government agencies

In justifying the tactics, the spy agency provided "inaccurate information" to the White House, Congress, the Justice Department, internal CIA investigators, the press and the public, the report found.

The CIA was faulted for giving bad information to the Justice Department from 2002 to 2007 about how interrogations were conducted and how effective they were.

Justice Department lawyers, working off the faulty information, concluded in 2002 that "necessity or self-defense" might justify torture.

In 2005, the CIA gave the Justice Department inaccurate examples of the effectiveness of its interrogations, the Senate report found. Justice Department lawyers concluded in 2005 and 2007 that the techniques were legal partly because they saved lives.

In 2005, the CIA gave the Justice Department inaccurate examples of the effectiveness of its interrogations, the Senate report found. Justice Department lawyers concluded in 2005 and 2007 that the techniques were legal partly because they saved lives.

The report also found that no CIA official, including two agency directors, told Bush about specific interrogation techniques until April 2006, at which point 38 or 39 detainees had already been subjected to them.

The report also raises questions about the accuracy of the 9/11 Commission's final report, published in 2004.

The commission suspected that critical information in its landmark report was the product of enhanced interrogation techniques, according to an NBC News analysis. Yet commission staffers never questioned the agency about the interrogation techniques, and ordered a second round of interrogations specifically to ask additional questions of the same detainees.

An NBC News analysis of the commission report found that more than one quarter of all footnotes in the 9/11 report refer to CIA interrogations of al Qaeda operatives who were subjected to the interrogation techniques. Information derived from the interrogations is central to the report's most critical chapters, those on the planning and execution of the attacks.

Strong reaction

The CIA, in a response that was filed last year but declassified this week, said that the Senate study was too flawed to serve as an official record of the CIA interrogation program.

It said that information gleaned from detainees in CIA custody "substantially advanced the Agency's strategic and tactical understanding of the enemy in ways that continue to inform counterterrorism efforts to this day."

A group of former CIA officials posted a response online, at the domain name CIASavedLives.com, and said that the Senate report contained factual errors and completely missed the context of the post-9/11 threat.

"It felt like a 'ticking time bomb' every single day," they said. "In this atmosphere, time was of the essence. We had a deep responsibility to do everything within the law to stop another attack."

Republicans on the intelligence committee issued their own report, describing the majority report as flawed in both fact and analysis and insisting that harsh interrogation had produced results, including the capture of al Qaeda suspects.

Sen. John McCain, R-Ariz., who was himself tortured during five years as a prisoner of war in North Vietnam, said that the report would strengthen the United States' standing in the world.

He said that terrorists could use the report as a justification for attacking Americans, "but they hardly need an excuse for that. That has been their life's calling for a while now."

"What might come as a surprise, not just to our enemies, but to many Americans, is how little these practices did to aid our efforts to bring 9/11 culprits to justice and to find and prevent terrorist attacks today and tomorrow."

The Justice Department said in a statement that it stood by its decision not to bring criminal charges after its own probe five years ago.

"That review generated two criminal investigations, but the Department of Justice ultimately declined those cases for prosecution, because the admissible evidence would not be sufficient to obtain and sustain convictions beyond a reasonable doubt," the department said.

A spokesman for Bush said that Bush had not seen the report and would have no comment.

'No nation is perfect'

In a statement, President Barack Obama credited the work of dedicated intelligence agents and said that the Bush administration had faced agonizing choices about how to protect the country after Sept. 11, 2001.

But he said that the report documented a "troubling program" of interrogation tactics that were "inconsistent with our values as nation."

"No nation is perfect," he said. "But one of the strengths that makes America exceptional is our willingness to openly confront our past, face our imperfections, make changes and do better."

The full report is estimated to be 6,000 pages. A much shorter executive summary from the Democratic majority, led by Feinstein, was declassified after months of dispute between the committee and the CIA.

U.S. military and diplomatic installations were put on alert ahead of the report because of the perceived risk that the details in the report will cause unrest. About 2,000 Marines were on standby to respond to threats against embassies or other interests.

Two days after he took office, in 2009, Obama reversed some Bush-era counterterrorism policies and ordered an end to coercive interrogation. He pledged to restore the United States to "moral high ground."