In late 1965, after a coup attempt whose circumstances remain murky, Indonesian society exploded into one of the paroxysms of mass killing that form a kind of grim leitmotif of twentieth-century life. Supported by the Indonesian army, conservative strands of Islam, and anti-Communist business interests, a purge of Communists in the government and army turned into a massacre fueled by communal hatreds. The best estimates of the carnage hold that between 500,000 and a million Indonesians were killed, but the entire subject remains a sensitive one in Indonesia, and no systematic accounting of what took place has ever been carried out.

Enter Joshua Oppenheimer, an American documentary filmmaker based in Denmark. A fluent Indonesian speaker who had come to southeast Asia to investigate the effects of globalization, he began to interview those responsible for the killings and found many of them proud of their roles because they believed they had stopped Communism in Indonesia. The killers from that time–small-time thugs, essentially–agreed to reenact the murders for Oppenheimer, who has said that his method “was not an elaborate lure to get them to open up. The method was a response to their openness.” He told them that he would film whatever they wanted to present.

So far, the banality of evil. But then it gets surreal. The film focuses mostly on a death squad leader in Sumatra named Anwar Congo, who recalled that the original killers imitated murder scenes from American films–and in fact were annoyed in the beginning that the previous left-leaning government had discouraged American film imports. Congo sets himself up as a director of the reenactment, casting the killings as gangster film scenes. His favorite method was to strangle a victim with a wire. Congo throws in Western sequences and even a song-and-dance routine in the countryside. The violence of American culture hangs over the scenes like a bad dream–and the extent to which the CIA was involved in the killings remains under debate.

It sounds bizarre until you realize that Congo and his cohorts are living well, having reaped benefits for decades from the corrupt military regime they helped install. But the pageant of self-justification begins to backfire on Congo when he plays a victim in one of the killing scenes. All through the film he has complained of nightmares, and at this point the old man begins to realize the enormity of his crimes–he is thought to have personally killed a thousand people. Many things in The Act of Killing are difficult to watch, but I’ve never seen anything more intense on film than the final half hour.

The Act of Killing has been nominated for the Oscar for best documentary. Plainly, it’s unlike any other documentary ever made. Oppenheimer, who himself was harassed by the Indonesian military and had nightmares himself during the making of the film, has called it “a documentary of the imagination,” but everything in it is true and still present. Don’t leave before the final credits, which make this clear in an unforgettable way.

The Act of Killing comes to the Michigan Theater March 12.