Blindfolded, hooded and wearing earmuffs, suspected terrorists were shackled and flown to secret interrogation centers. The buildings themselves were quiet, clinical and designed to fill prisoners with dread. Detainees were shaved, stripped and photographed nude.

The questioning began mildly, a shackled detainee facing a non-threatening CIA interrogator. But for detainees who refused to cooperate, the interrogation escalated in terrifying ways.

Few people have ever witnessed the process, which was designed to extract secrets from "high value" suspects during the years after the Sept. 11, 2001, terrorism attacks on the U.S. But Justice Department documents, which the Obama administration simultaneously released and repudiated Thursday, describe the process from darkness to waterboarding in skin-crawling detail.

Prisoners were naked, shackled and hooded to start their interrogation sessions. When the CIA interrogator removed the hood, the questioning began. Whenever the prisoner resisted, the documents outlined a series of techniques the CIA could use to bring him back in line:

• Nudity, sleep deprivation and dietary restrictions kept prisoners compliant and reminded them they had no control over their basic needs. Clothes and food could be used as rewards for cooperation.

• Slapping prisoners on the face or abdomen was allowed. So was grabbing them forcefully by the collar or slamming them into a false wall, a technique called "walling" that had a goal of fear more than pain.

• Water hoses were used to douse the prisoners for minutes at a time. The hoses were turned on and off as the interrogation continued.

• Prisoners were put into one of three in "stress positions," such as sitting on the floor with legs out straight and arms raised in the air to cause discomfort.

At night, the detainees were shackled, standing naked or wearing a diaper. The length of sleep deprivation varied by prisoner but was authorized for up to 180 hours, or 7 1/2 days. Interrogation sessions ranged from 30 minutes to several hours and could be repeated as necessary and as approved by psychological and medical teams.

Some of these techniques, such as stripping a detainee naked, depriving him of sleep and putting a hood over his head, are prohibited under the U.S. Army Field Manual. But in 2002, the Justice Department authorized CIA interrogators to step up the pressure even further on suspected terrorist Abu Zubaydah.

Justice Department lawyers said the CIA could place Zubaydah in a cramped confinement box. Because Zubaydah appeared afraid of insects, they also authorized interrogators to place him in a box and fill it box with caterpillars (that tactic ultimately was not used).

Finally, the Justice Department authorized interrogators to take a step into what the United States now considers torture, waterboarding.

The Bush administration approved the use of waterboarding, a technique in which Zubaydah was strapped to a board, his feet raised above his head. His face was covered with a wet cloth as interrogators poured water over it.

The body responds as if it is drowning, over and over as the process is repeated.

"We find that the use of the waterboard constitutes a threat of imminent death," Justice Department attorneys wrote. "From the vantage point of any reasonable person undergoing this procedure in such circumstances, he would feel as if he is drowning at the very moment of the procedure due to the uncontrollable physiological sensation he is experiencing."

But attorneys decided that waterboarding caused "no pain or actual harm whatsoever" and so did not meet the "severe pain and suffering" standard to be considered torture.

President Barack Obama has ended the CIA's interrogation program. CIA interrogators are now required to follow Army guidelines, under which waterboarding and many of the techniques listed above are prohibited.

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