Here's a link to the truly remarkable investigative piece by Jane Mayer in the current New Yorker on the CIA's secret "black sites" and what kind of torture went on there. Although a bit longish (11 pp. in print-friendly format) it's worth reading in its entirety.
Essentially Jane demolishes the cover story that whatever unpleasant stuff might have gone on at Abu Ghraib or Guantanamo was the work of low-level "rogue" guards who have been tried and punished. She describes a systematic and rigorous program -- remarkably tightly controlled and disciplined from the tops; it seems techniques and plans had to be approved, probably by the CIA director himself, on a day-to-day basis -- of extremely abusive interrogation approved at the highest levels of government. What's a little shocking is that the interrogation program was implemented "on the fly" by an agency that had no practical experience in interrogation or running prisons, and how quickly just about everyone involved seemed to assume that torture would be necessary. But people-pleasing George Tenet just couldn't say "no." How ironic that the people-pleasers end up authorizing the most people-torturing policies.
The other key is that the program of inflicting "learned helplessness" on detainees through waterboarding, sleep deprivation, isolation, prolonged periods in "dog cages" too small to stand up in, hanging from wrists and the like, despite all the claims by officials that is was essential to gathering key information that might have prevented another attack, in fact produced what one officer called 90 percent unreliable information. There's no real science behind the concept that torture can produce valuable truth in an imminent-danger situation. It's hard not to conclude -- my conclusion, not Jane Mayer's, who confines herself to fact and is careful to let you know when she doesn't know or her information is based on hearsay -- that the main reason for torture is sadism or vicarious sadism, n0t anything remotely resembling national security.