It’s difficult not to be ambivalent about “The Act of Killing,” a documentary that reveals the horrors of the Indonesian campaign against communists and other “undesirables” like ethnic Chinese, which extends back for decades but is still being waged by powerful paramilitary groups. But it does so from the perspective of self-styled “gangsters” who were among the most vicious perpetrators in the initial stages of the operation in 1965-66 and are now making a movie dramatizing what they did (they’re all big fans of Hollywood movies and try to emulate them)—as well as continuing their corrupt activities.

On the one hand, publicizing the grotesque deeds of the murderers has a certain salutary effect, even if they’re beyond legal punishment. But watching them live out their days in comfort and—for the most part—smug contentment is galling. And when the film shows one of them haunted by what he’s done, even if only sporadically, it moves in the direction of sympathy for the killers along with their victims that’s deeply unsettling. (Indeed, in their film they sometimes play their victims, suggesting a convergence between killer and killed that’s morally repugnant.) The imbalance is accentuated by the fact that the only victims we actually see are Chinese shopkeepers being shaken down by the gangsters; there’s no actual footage of the events of nearly half a century ago, or interviews with survivors or their relatives and friends.

Of course, disturbing us is what the picture—directed by Joshua Oppenheimer—is all about. “The Act of Killing” is a shocking exhibition of what Hannah Arendt called the banality of evil—or, in this case, the absurdity of evil. The principal focus is on Anwar Congo, an elderly, genteel fellow who, along with his gruffer, heavier colleague Herman Koto, describes how they transformed themselves from penny-ante crooks scalping movie tickets to hardened killers instrumental in the liquidation of hundreds, if not thousands. (Estimates of the total number of “disappeared” in the Indonesian slaughter range from half a million to more than two and a half million.) He’s particularly proud of inventing a method of execution with a wire noose that was extremely efficient while resulting in less bloodletting—and clean-up—than other methods.

Congo, Koto and their associates—including a publisher who identified people for interrogation that inevitably led to execution—are generally eager to talk about what they did, arguing that it was absolutely necessary for the safety of the state. And in sequences that are frequently bizarre, featuring dancers emerging out of the mouth of a statue shaped like a fish, Herman donning a flamboyant red dress and Carmen Miranda headgear, and Congo posing in a long robe in front of a waterfall—as well as recreating torture scenes and a massacre at a village—they demonstrate how they’re memorializing their accomplishments on celluloid. They appear on TV talk shows to discuss their project with smiles, feeling no apparent need to offer any justification. There’s a surrealistic tone to it all, especially since we’re also shown government ministers openly courting the militias that arose out of their actions and continue to abuse the population in the present day.

And yet there are strangely discordant moments in which some subjects pull back from the general sense of enthusiasm for the killing while preening about their role in it. An official wonders whether the graphic recreation of a mass slaughter will tarnish the image of the Pancasila paramilitary group that conducted it, although he then opines that they could have been even more brutal. An old associate of Congo’s, who cynically notes that history is written by the winners, who determine what’s right and wrong, also points out that by dramatizing what they did, they might encourage sympathy for the victims, whom they’ve always described as the cruel ones. A lower-ranking member of the gang recounts the murder of a relative in a hysterically giddy recitation while suggesting in might be written into the script. And the film closes by juxtaposing a scene in which Congo brings his little grandsons into his family room to watch footage of a sequence in which he plays a torture victim with another in which he revisits the place where he killed the actual ones and begins gagging uncontrollably over the recollection.

What’s to be made of this? “The Act of Killing” opens with a quotation from Voltaire, who noted that murder is something that must be punished—unless it’s mass murder done for the “public good,” in which case it’s glorified. That certainly seems the case with the Indonesian massacres, which the perpetrators, and the nation, have never had to confront as moral atrocities. Does Oppenheimer intend his film to be at least the beginning of the sort of reexamination that could exorcize some of the country’s demons? Or is it merely a confirmation of the fact that, as Agatha Christie opined in the title of one of her mysteries, “Murder is Easy”?

Whatever the intent, “The Act of Killing” is neither easy to watch or to unpack. But it will certainly not leave you unmoved, though the feelings it engenders will be complicated.