The perpetrators of genocide featured in “The Act of Killing” pretend they’re in a musical.

The poster for “The Act of Killing” features a wide shot of a fake giant fish nestled in an Indonesian jungle with pink-clad figures emerging from its mouth. Which is strange, particularly given that the film is about genocide.

After director Joshua Oppenheimer decided to make a documentary about Indonesia’s 1965-66 genocide, he spent seven years in and out of Indonesia filming dozens of perpetrators of the country’s mass killings. The main subject of the film is Anwar Congo, one of the leaders of the regime’s death squads. Besides the usual talking-head interviews, the film shows Congo and his compatriots as they re-enact the killings, with each scene filmed in the style of a particular genre of American film. (Since none of the death-squad leaders in Congo’s circle were women, one of the men takes on most of the female roles.)

“Each [re-enactment] is an insistence that [the killings] don’t mean what they mean,” Oppenheimer says. “You can’t make a cowboy scene with a man in drag about murder and not be in denial about what you’ve done. So each re-enactment is an attempt [by the perpetrators] to replace the trauma.”

In one chilling scene, Congo volunteers to play the victim of a “Godfather”-style killing in which he’s strangled with wire (a technique Congo brags about perfecting early on in the film). After watching the performance, he tells the off-camera Oppenheimer that doing the scene made him feel what his thousands of victims felt. Oppenheimer challenges him, pointing out that Congo knew he wasn’t going to die and could call “cut” at any time.

“Throughout the film I was able to step in and be honest,” Oppenheimer says. “That openness characterized my relationship with them from the beginning.”

The most remarkable thing about the film, which opens Friday at the Landmark E Street Cinema, is that Oppenheimer’s relationship with the perpetrators (he gets them to admit to some jaw-dropping crimes) works in tandem with the fictionalized, highly stylized re-enactments; the rather cheesy acting and sets of the narrative sections are in stark contrast to the talking-head segments that describe what actually happened.

“After interviewing the first 10 or 15 [perpetrators], I realized I did not have to be circumspect,” he says. “They would immediately begin boasting. I started to wonder: Why are they boasting? How do they want to be seen by the rest of the world? How do they see themselves? The re-enactments answer the question: How do you want to be seen?”

And the answer? As movie stars.