A common misconception among viewers is that Oppenheimer somehow tricked the killers and their associates into participating in the film—that he told them he was making a film that would celebrate them, or that he wanted to make them stars in an action movie. This misconception is based on the perfectly logical notion that anyone who had taken part in such an atrocity would understand the danger of admitting to war crimes on camera. But these men had never been accused of anything; they were heroes. And while Oppenheimer sometimes had to hide his disgust at the casualness, or even joy, with which the men relived their deeds, he never had to be anything but honest about his intention to make a film that highlighted their role as mass murderers.

As he continued to film, Oppenheimer became fascinated by what he called the killers’ “performance of impunity” and was convinced that the image they presented in the re-enactments—more than the slaughter they were re-enacting—was the most compelling story of all. The suffering and oppression of the victims could tell a story about the margins of Indonesian society. But the performance being staged for Oppenheimer, by men praised for decades as the saviors of modern Indonesia, told a story about the society’s dominant identity and beliefs.

In 2005, Oppenheimer began what became the eight-year process of making The Act of Killing. He set out to do the exact opposite of what journalism typically tries to do. As he told me in July, “Whenever you talk to somebody as a journalist, they stage themselves for you. They think, ‘How do I want to be seen by the world?’ And we try to get past that and extract from those interviews information that we can treat transparently. But we’re throwing away a great resource. Because in the moment of someone presenting themselves, in that self consciousness, is something also worth exposing: What is the image that they have of themselves?”

If the killers present themselves as national heroes, and this idea has become central to Indonesia’s sense of itself, and a way to legitimize its power structure, then understanding that façade is crucial to understanding the massacre and the corrupt system that grew out of it. The point of making a film that focused on this artifice, Oppenheimer says, “was to show the stories we tell ourselves about who we are, that [in turn] make our reality what it is. And to put reality through a kind of prism whereby all these different narratives that make up the surface are visible.” The re-enactments trace the imagining of mass murder to the self-image of a society, using the words of the killers themselves to make that seemingly remote connection horrifyingly apparent.

Oppenheimer filmed with 40 executioners before he met Anwar Congo, the main subject of The Act of Killing, and the man with whom he would refine his use of re-enactment as a documentary technique. Introduced at the beginning of the film with a title card that reads simply, “Executioner in 1965,” Congo is a corpse-thin, grandfatherly figure with a mischievous smile. His paternal air is heightened by the constant presence of his protégé, Herman Koto, a comically fat gangster and paramilitary leader who, while too young to have participated in the 1965 massacre, embodies its legacy.

One of the most-feared death-squad leaders in North Sumatra at the time of the massacre, Congo killed as many as a thousand people using nothing but a length of wire, a club, or a machete. His response to Oppenheimer’s challenge was to cast himself as the hero in scenes inspired by the Hollywood genres he enjoyed in his youth. By allowing Congo to indulge in this absurdity, Oppenheimer learns far more about both the man and his society than he ever could have learned from hours of interviews.

Michael Meyer is a CJR staff writer.