The "dark side" of the title is the figurative arena where Dick Cheney, in an appearance on Meet the Press that took place five days after 9/11, ominously hinted that the war against terror will be largely fought — a shadowy realm where "sources and methods that are available to our intelligence agencies" will be used against our enemies. The implication was clear: We were now dealing with some very bad people, and the Bush White House wasn't about to allow its hands to be tied by the usual rules of engagement or international wartime conventions. The "taxi" is the vehicle once driven by Dilwar, a slightly built, 22-year-old Afghan cabbie from the small farming village of Yakubi who disappeared into that dark side in December 2002 after he and his three passengers were stopped by Afghan militiamen anxious to curry favor with the U.S. forces. On December 5, 2002, Dilwar arrived at the Bagram Theater Internment Facility, a Soviet-era structure that had been converted into a U.S. prison. Five days later, Dilwar was dead, the cause of death officially noted as a homicide. According to the army medical examiner, the 120-pound young man had been shackled and suspended from a metal grate for days, and his lower extremities so badly pummeled that his legs had been "pulped"; had he not died, Dilwar's legs would have had to be amputated. Dilwar, known as Detainee 421, was not the first prisoner to die in Bagram — a week earlier, a Muslim mullah named Habibullah was also killed when similar blows to his thighs resulted in a fatal blood clot — but acclaimed documentary filmmaker Alex Gibney (ENRON: THE SMARTEST GUYS IN THE ROOM) uses the cabdriver's death as a marker to help chart the course that the use of torture has taken since Cheney's dark war began. According to Gibney's film, Dilwar's killing represents a tragic midway point between the treatment of enemy combatants at the military detention camp in Guantanamo Bay, Cuba, and the abuses committed against Iraqi prisoners inside Abu Ghraib. It's the film's thesis that the course describes an arc according to which torture was redefined, encouraged, employed, officially denounced from above, then unofficially allowed to recur again and again on the ground, eventually resulting in the kind of shocking scenes captured in those infamous photos taken at Abu Ghraib. All the while, what one interviewee calls a "fog of ambiguity" surrounding what was and wasn't officially authorized shielded superior officers and key members of the Department of Defense — namely Donald Rumsfeld — from accountability while leaving ordinary soldiers holding the bag. Gibney and his panel of knowledgeable interviewees make a number of convincing arguments, including an important one against the efficacy of torture. The parade of images Gibney has assembled, many of which are seen here in full color for the very first time, amounts to an atrocity exhibition that's difficult to watch, but demands to be seen.