The infamous photos of torture at Abu Ghraib prison in Iraq that became public in the spring of 2004 — a pyramid of naked prisoners, a hooded man forced to stand in a crucifixionlike pose, a cowering man on a dog leash — were evidence not of just a “few bad apples” among the prison guards but, as an Army investigation found, documentation of a systemic problem: Military personnel had perpetrated “numerous incidents of sadistic, blatant, and wanton criminal abuses.” The abuses had roots in decisions made at the highest levels of the Bush administration, which asserted that the United States need not abide by the Geneva Conventions in its war on terror.

Powerful and damning accounts of the Bush administration’s determination to work what Vice President Dick Cheney called “the dark side” and its elaborate efforts to legalize torture (including arduous attempts to narrowly define torture as leading to “serious physical injury so severe that death, organ failure or permanent damage” is likely to result) can be found in two essential books, “The Torture Papers: The Road to Abu Ghraib,” edited by Karen J. Greenberg and Joshua L. Dratel, and “Standard Operating Procedure,” by Philip Gourevitch and Errol Morris. An important personal perspective is now provided by Eric Fair’s candid and chilling new book, “Consequence,” which is at once an agonized confession of his own complicity as an interrogator at Abu Ghraib and an indictment of the system that enabled and tried to justify torture.

Mr. Fair, who worked for CACI, a private contractor that provided interrogation services at the prison, participated in or witnessed physical abuse, sleep deprivation and the use of what he calls “the Palestinian chair” (a monstrous contraption that forces a prisoner to assume an excruciating “stress position”). He sees naked men handcuffed to chairs, stripped of their dignity and their clothes. He and his colleagues “fill out forms and use words like ‘exposure,’ ‘sound,” ‘light,’ ‘cold,’ ‘food’ and ‘isolation’” — ordinary words that become shorthand for methods of inflicting fear and pain. He rips a chair out from underneath a boy and shoves an old man, head first, into a wall.

Of the Abu Ghraib torture photos broadcast by “60 Minutes” in April 2004, Mr. Fair writes: “Some of the activities in the photographs are familiar to me. Others are not. But I am not shocked. Neither is anyone else who served at Abu Ghraib. Instead, we are shocked by the performance of the men who stand behind microphones and say things like ‘bad apples’ and ‘Animal House’ on night shift.’”

In 2007, Mr. Fair says, he confessed everything to a lawyer from the Department of Justice and two agents from the Army’s Criminal Investigation Command, providing pictures, letters, names, firsthand accounts, locations and techniques. He was not prosecuted. “We tortured people the right way,” he writes, “following the right procedures, and used the approved techniques.”

Mr. Fair, however, became increasingly racked by guilt. He begins having nightmares. Nightmares in which “someone I know begins to shrink,” becoming so small “they slip through my fingers and disappear onto the floor.” Nightmares in which “there’s a large pool of blood on the floor” that moves as if it’s alive, nipping at his feet.

His marriage starts to unravel. He drinks heavily despite a heart condition that threatens his health. When his best friend from Iraq, Ferdinand Ibabao, is killed by a suicide bomber in Baghdad, Mr. Fair thinks that maybe he, too, deserves to die there. He returns to Iraq for another tour — this time, in a job with the National Security Agency.

Mr. Fair recounts all this in understated, staccato prose. He tells us about the important role the church played in his childhood in Bethlehem, Pa. He tells us about his dreams of becoming a police officer, or maybe a pastor. And he tells us about the odd twists and turns that took him to Iraq as an interrogator.