Nearly a year ago, when “Taxi to the Dark Side” first devastated audiences at the Tribeca Film Festival, director Alex Gibney expressed a simple aspiration when speaking to one downtown festival audience: “I hope it provokes some rage.” Well, to borrow a quote from his less-than-favorite politician: Mr. Gibney, “mission accomplished.”

Mr. Gibney’s film, which arrives in theaters Friday, became a hit on last year’s festival circuit and has long been considered a contender for a documentary Academy Award nomination. But the film is no less germane today than it was on the day Mr. Gibney unveiled it in TriBeCa. Several years after such terms as “waterboarding” became staples in our national debate over security and over which forms of interrogation are appropriate in our war on terror, many of the implications of using torture as a standard technique have been lost in partisan bickering and electoral politics.

Much as he did in his Oscar-nominated breakout of 2005, “Enron: The Smartest Guys in the Room,” Mr. Gibney seems chiefly interested today in what it takes for ordinary men to operate at the outer extremes of common decency. In fact, the executives in the former film, who were left to their own devices and shattered thousands of lives in a fit of unchecked greed and arrogance, bear more than a passing resemblance to the American soldiers in “Taxi to the Dark Side,” who were dropped into foreign interrogation rooms and were instructed simply to “get the information.”

The titular “taxi” is a real one, and the story of its driver — a man named Dilawar — offers Mr. Gibney a platform on which to engage this underside of American foreign policy. An Afghan taxi driver who was captured by militiamen in 2002 in exchange for a cash payment, Dilawar was turned over to American forces and then taken to Bagram Air Force Base, where he was identified as the triggerman behind an insurgent rocket attack in the region. He was beaten so severely so that his legs became pulpified. Had he lived, they would have required amputation. On the certificate that was handed over to Dilawar’s family, the cause of death was listed as “homicide.” But in official statements, the Army said Dilawar died of natural causes. After the American press, and later Mr. Gibney, tracked down the Afghan’s family and took photographs of the death certificate, the Army staged a trial for a few of the men in charge of Dilawar’s interrogations. This is where the indignation of “Taxi to the Dark Side” truly sets in, as it witnesses the way the buck is passed down the chain of command.

The more Mr. Gibney interviews the soldiers involved, the more their lack of concrete directives seems like an implicit acknowledgement of just how terrifying these interrogations have become. The Army, it appears, left these rank-and-file soldiers to their own devices, demanding more and more from them before feeding them to the wolves when the violent results came to the world’s attention.

Mr. Gibney succeeded in lining up a number of high-ranking interview subjects, from the renowned law professor John Yoo to Senator Levin of Michigan, but his most blunt, shocking, and scathing material comes from the low-ranking interrogators who worked at places such as Bagram. Their testimony reveals a flawed and dreadfully closed system — a world of prisoners and interrogators that is all but detached from such concepts as the right to habeas corpus, the tendencies of human nature, and the actual effectiveness of torture techniques. Ironically, nowhere in this cycle of mercenaries and hooded prisoners is the truth assigned a value.

More than 90% of the prisoners at Bagram were turned over by mercenaries seeking a reward, and it is chilling to hear those involved recall the standard operating procedure. Vindictive Afghan farmers could simply turn their neighbors over to the Americans as a way of securing reward money and eliminating competition.

In the film, one interrogator concedes that he knew that the majority of prisoners placed in front of him were not terrorists, and that when he was ordered to conduct a two-hour aggressive interrogation, he would instead yell gibberish at the inmate — at one point reading the nutritional facts off the side of a cereal box — to pass the time.

The most harrowing moment of the film is saved for the closing credits, when Mr. Gibney interviews his own father, himself a World War II interrogator, about this torture debate, and witnesses an angry and passionate tirade of indignation. Frank Gibney simply cannot comprehend the compromises of principle that have been made in our hunt for the people who damn us for those very principles.

If his is the angriest aside to be found in “Taxi to the Dark Side,” then the most haunting, and educational, sequence involves an array of torture photos and videos that, together with the testimony of several on-screen experts, evokes the awesome power of psychological torture and the degree to which physical harm pales in comparison. Well before most prisoners in Afghanistan, Guantanamo Bay, and elsewhere are interrogated physically, they are broken down psychologically, subjected to such techniques as sleep interference, stress positions, and sensory deprivation. And as outlined by Mr. Gibney, it takes only a few days of sensory deprivation for a subject to experience irreversible mental damage.

Near the end of “Taxi,” Mr. Gibney hints at the fallout: When these hundreds of men and boys go back to their families, shattered shells of their former selves, they will become an army of enraged souls, vowing vengeance. If they weren’t terrorists going in, a good number of them will be if and when they come out.

ssnyder@nysun.com