"Something really bad happened here." So begins Army interrogator Tony Lagouranis's first briefing at Abu Ghraib. While Lagouranis's training stressed the rules of the Geneva Conventions, once in Iraq, he discovered that pushing the legal limits of interrogation was encouraged. Under orders, he-along with numerous other soldiers-abused and terrorized Iraqis by adding "enhancements" like dogs, hypothermia, and other techniques to "Fear Up Harsh"-the official tactic designed to frighten prisoners into revealing information. And he saw others do far worse.

The first Army interrogator to...