Lest there be anyone laboring under the delusion that the abuse of detainees at the Bagram Air Base in Afghanistan – and, later, at the Guantánamo Bay detention center and Abu Ghraib – was the work of “a few bad apples,” Taxi to the Dark Side cites a wealth of damning evidence to the contrary.

Written and directed by Alex Gibney, who previously examined white-collar corruption in Enron: The Smartest Guys in the Room, Taxi is difficult to watch, as any document of torture must necessarily be. But it is essential viewing for those wishing to understand how the Bush administration’s War on Terror has affected America and its image abroad. It begins with a single instance of wrongdoing – the unjustified arrest of a 22-year-old Afghan taxi driver named Dilawar, who would be found murdered in his Bagram holding cell just five days later – and uses it to illustrate how government-sanctioned brutality became a matter of policy.

Dilawar, as it turned out, had no ties to either al-Qaida or the Taliban. Taken into custody by Afghan authorities eager to collect U.S. reward money for terrorist sympathizers, he was bound and beaten to the point that his legs were quite literally shattered – had he survived, both would have required amputation. The American servicemen implicated in his death speak frankly about their role in the murder of an innocent, but these are not the chilling confessions of born killers. They are the candid, unflinching observations of men led to savagery by superiors with no regard for the humane restraints of the Geneva Convention.

It was Vice President Dick Cheney, after all, who ominously predicted that the U.S. would need to visit the “dark side” to dismantle the terrorist infrastructure in the Middle East. Through a series of interviews and archived news footage, Taxi allows the architects of American military policy – men like former Justice Department official John Yoo and former Defense Secretary Donald Rumsfeld – an opportunity to rationalize their spirited defenses of torture in the form of sexual humiliation, physical abuse and sensory deprivation. Still, there is never any doubt where Gibney’s sympathies lie.

But Taxi to the Dark Side, though selective in its details, is no overheated polemic. It is dispassionate, lucid and painstakingly thorough, tracing the origins of modern techniques of torture and following the practices’ long and legally ambiguous journey into U.S. prisons in Iraq, Afghanistan and Cuba. For those willing to go along for the ride, it is a harrowing experience, as Gibney makes his case that the United States, in its haste to retaliate for the atrocities of 9/11, has itself crossed a bloody line in the sand.