Their transformations took place in a sensory cocoon: aboard a CIA aircraft, shackled in place, deprived of sight and sound by blindfolds, headsets and hoods.
They emerged into an existence that was hidden for most of the last eight years, but now is possible to glimpse through dozens of declassified files released by the Obama administration last week.
Scattered throughout, in the CIA's clinical style, are descriptions of the prisoners' surroundings, the extraordinary security measures with which they were handled, the often brutal search for answers they were thought to possess, and what passed for everyday life.
Some days seemed endless, illuminated around the clock by a pair of 17-watt fluorescent bulbs. White noise from the walkways filtered through the cell walls usually "in the range of 56-58" decibels, about as loud as people generally talk.
There were touches of CIA hospitality. Prisoners were given books, movies and checkerboards to pass the time. They could hit the gym for exercise, and let their hair grow as long as they liked.
But there were also long stretches designed to break prisoners' will.
They were stripped, shaved and shoved against walls the moment they arrived. What came next was an escalating menu of interrogation options, culminating in a method used in the Inquisition -- waterboarding -- to make them think they would drown.
The purpose, of course, was to make them talk. The Bush administration said the United States was in danger of additional assaults after the attacks of Sept. 11, 2001. CIA interrogators were under orders to get a lot of information, fast. Whether the harsh interrogation methods were necessary to gather the intelligence is still a matter of dispute.
The only glimpse?
The secret overseas "black sites" where the CIA conducted the interrogations are empty now, if not already dismantled. They were never examined by a congressional committee, nor inspected by the international Red Cross.
"These papers may provide the only picture that history gets of what life was like in these facilities," said Tom Malinowski, Washington director of Human Rights Watch.
The black sites not only imprisoned men but reduced them to a near helpless state. The aim, as outlined in one document, was to teach every detainee "to perceive and value his personal welfare, comfort and immediate needs more than the information he is protecting."
The prisoners' arrival -- almost always in diapers -- was engineered to achieve that end.
After being shaved, stripped and photographed nude, detainees were examined by CIA medical and psychological personnel. Then came a preliminary interrogation that would determine the prisoners' fate.
Only those considered extremely cooperative would avoid a trio of techniques designed to produce a "baseline, dependent" state: the deprivation of clothes, solid food and sleep.
Follow-up sessions would start with the prisoner standing with his back against a wall and a towel or collar to prevent whiplash wrapped around his neck. He could be thrown against the wall just once "to make a point, or 20 to 30 times consecutively."
Prisoners so abhorred the repeated slamming that they would remain in so-called stress positions, such as painful kneeling postures, for hours to avoid a return to the wall, according to one Dec. 30, 2004, memo that amounts to a CIA blueprint for breaking a detainee's will.
The rules for administering such methods were spelled out precisely. Detainees could be kept in a large box for 18 hours a day, but small boxes for only two hours at a time. They could be hosed with water for 15 minutes, but the air temperature had to exceed 65 degrees if they weren't to be given a towel.
The detainee "finds himself in the complete control of Americans," the memo said. "The procedures he is subjected to are precise, quiet and almost clinical."
Earlier this year, the Obama administration released a series of Justice Department memos laying out legal rationales for the array of coercive interrogation methods the CIA employed.
The documents -- including an internal report by the CIA inspector general and correspondence between the agency and the Justice Department -- show that the agency also sought Justice Department review of the basic conditions in which prisoners were kept.
The agency had to use extraordinary security measures inside the prison walls, the records indicate, because keeping the facilities' purpose secret meant the CIA could not surround them with guards and barriers that would attract attention from the public.
The black sites "were not designed as ordinary prisons, much less as high-security detention centers for extremely dangerous, and often highly sophisticated, international terrorists," one Justice Department memo said. "They are a serious risk to escape and to the safety of CIA personnel."
About 100 prisoners passed through the CIA system. Among them were a handful of "high-value detainees" including Khalid Shaikh Mohammed, self-proclaimed mastermind of the Sept. 11 attacks.
Some detainees attacked guards, according to the documents, and the sites themselves were also seen as potential targets for terrorist attacks.
The records don't say where the prisons were, but news reports and accounts from former U.S. officials indicate the sites included Thailand, Poland, Romania, Morocco and Lithuania.
Internal security measures included the "white noise" in the prison walkways to prevent detainees from communicating. The upper limit was 79 decibels -- about the level of a garbage disposal -- to avoid permanent harm to detainees' hearing.
Prisoners were kept in solitary confinement and allowed no communication with the outside world. Any time they were moved, they were shackled and outfitted in blacked-out goggles to prevent them from seeing the layout of the prison, or getting any clues to where it was.
Their cells were illuminated and monitored via closed-circuit video 24 hours a day. "Some detainees are provided eyeshades to permit them to block out the light when they are sleeping," an Aug. 31, 2006, Justice Department memo said.
In some sections, the memos seem contradictory, describing ways to reduce prisoners to an infantile state while insisting that the agency be committed to "minimizing the physical discomfort and psychological distress that detainees are likely to suffer."
As a result, after prisoners were broken by a regimen of sleep deprivation, slamming them against the wall, and in three cases waterboarding, they were often given items to ease their sense of isolation. Among them were "a wide variety of books, puzzles, paper and 'safe' writing utensils, chess and checker sets, a personal journal, and access to DVD and VCR videotapes."