An optometrist fits an elderly man for glasses. Their seemingly idle conversation turns to the mass killing that occurred in their village nearly 50 years ago. The older man readily admits that he personally rounded up and murdered dozens. The optometrist says, "My brother was one of them."

It may sound like a Kafka parable, but this harrowing scene repeats itself, with variations, throughout the new documentary The Look of Silence, director Joshua Oppenheimer's follow-up to his Oscar-nominated The Act of Killing (2012). Unlike many documentaries on unpleasant subjects, Silence isn't an ordeal you undergo for the information value. It's no upbeat experience, but it is always absorbing, and it is sometimes disturbingly beautiful.

Oppenheimer does not pretend to have a neutral lens. "I see documentary not so much as the transparent window onto reality," he told the Dissolve in 2014. "It's better thought of as a series of occasions, created between the filmmaker and the subject." What that means is that he places his subjects in unnatural situations. For The Act of Killing, he persuaded the ringleaders of the 1965-66 mass killings of communists and ethnic Chinese in Indonesia to reenact their violence for his camera. The results included surreal spectacles and unsettling revelations about the human capacity to shrug off responsibility for others' suffering.

Killing shows us the perpetrators of the massacres — who remain in power — living side by side with survivors, but it could leave some viewers with the impression that almost everyone in Indonesia has shrugged off the past. The Look of Silence dispels that notion.

Here Oppenheimer has an on-screen partner: the optometrist, Adi, whose life was shaped by his brother Ramli's murder before he was born. After Adi views Oppenheimer's footage of the boastful perpetrators — an obviously staged sequence — he sets out to confront them. The situations are ambushes, but there's nothing Michael Moore-ish about Adi's approach. The film's title refers to his calm, steady gaze as he allows his interlocuters to incriminate themselves — a silent reproach that should induce remorse but rarely does.

Adi becomes the viewer's stand-in, his face fleetingly registering horror and incomprehension as the murderers unveil their justifications and their coping strategies. The killings of nearly a million people were just politics, explains an Indonesian legislator. (A TV news clip from the era suggests that many Cold War Americans saw the massacres similarly — as excesses justified by the worldwide battle against communism.) A former death-squad leader acknowledges that the gory memories have driven some of his colleagues to madness. Yet he has remained immune. "If you drink human blood," he explains sagely, "you can do anything" — a statement that sounds like a tough-guy metaphor, except he means it literally.

Some viewers may ask why Oppenheimer doesn't flesh out the victims: We learn more about the grotesque manner of Ramli's death than about his life. In places where another documentarian might use talking heads to establish that the communists were not actually human filth (as the killers keep insisting), Oppenheimer instead gives us silent visual meditations on the tropical landscape, or arty close-ups of cobwebs or Mexican jumping beans.

But do we really need character witnesses to tell us that the murder by machete of thousands of unarmed prisoners isn't justified, anywhere or for any reason? The filmmaker has said that he avoids painting the victims as saints so as not to offer his audience "the false reassurance that ... we are nothing like perpetrators." A meditation on the many uses of silence, this film could make us recall the times when we, too, speciously justified others' suffering — or chose to ignore it.

Attendees can ask Oppenheimer about his approach during a Skyped Q&A following the Vermont International Film Festival screening on Saturday, October 31, 1 p.m., at Main Street Landing Performing Arts Center in Burlington. More info at vtiff.org.

Correction 10/28/15: An earlier version of this review featured a photo from another film; the photo is now correct.