In the fall of 1965, the Indonesian military began a coup against the government. Over the next year, the army systematically eliminated its opponents — including union members, landless farmers, intellectuals, and the ethnic Chinese who were declared “Communists” and led to their deaths. Self-declared “gangsters” and paramilitaries executed between 100,000 and 2 million people; estimates vary widely because few records were kept, and because those guilty of the killings have remained in power ever since, making no secret of their past.

When Joshua Oppenheimer started interviewing the Indonesian killers for his documentary, The Act of Killing, he found men eager to boast about what they’d done. One, the nattily dressed, seemingly avuncular Anwar Congo, demonstrated an improvised garrote he’d created, then broke into an elegant dance routine. He told Oppenheimer that Elvis Presley musicals put him in a great mood for killing. Recognizing how cinema had influenced Anwar and his fellow gangsters, the filmmaker proposed a unique sort of collaboration: the killers would re-enact their crimes for Oppenheimer’s cameras, through whatever story or genre they thought appropriate.

The result is a disconcerting experience, where death-squad leaders play their victims in film noir-inflected scenes, or receive medals from the imagined dead in hallucinatory musical numbers. They ham it up for the camera, then pensively wonder if they’re revealing too much. Anwar plays himself as outwardly happy, but creates a fearsome, demonic spirit that he says visits him in dreams. Throughout it all, Oppenheimer’s “documentary” floats somewhere between fiction and reality, a fever dream of history, murder, and guilt.

The decade-long project drew the attention of both Werner Herzog and Errol Morris, who signed on as executive producers; Herzog called it “so powerful, so frightening, and so surreal, it would take a decade until you see another film of that caliber.” Oppenheimer has since taken The Act of Killing around the world, leaving many audiences equally stunned. With the film beginning to screen across the US, Oppenheimer discusses the relationship between storytelling and guilt, what it’s like to visit a society where killers are not shunned but admired, and how the next generation of Indonesians are dealing with their collective past.