In July 1995, the Bosnian Serb army, under the command of Gen. Ratko Mladic, overran the town of Srebrenica, which had been declared a safe haven by the United Nations. Muslim civilians sought refuge at a nearby U.N. base, but were handed over to Mladic’s soldiers, who separated them by gender and loaded them into buses and trucks. Around 8,000 men and boys were murdered, their bodies buried in mass graves, in one of the worst atrocities of the wars that convulsed the former Yugoslavia for much of the decade.

At the time, many in the West wondered how this could happen — how genocidal violence could erupt in Europe barely 50 years after the end of World War II. “Quo Vadis, Aida?,” Jasmila Zbanic’s unsparing and astonishing new film, shows precisely how. This isn’t the same as explaining why, though Zbanic’s granular, hour-by-hour, lightly fictionalized dramatization of the events leading up to the massacre sheds some glancing light on that question.

Mladic (Boris Isakovic) is an unnervingly familiar figure. A self-infatuated bully who travels everywhere with a cameraman, he punctuates his displays of power with litanies of grievance. But the movie isn’t really about him. He and his officers may be the authors of the nightmare, but the viewer suffers through it in the company of Aida Selmanagic (Jasna Duricic), who works as a translator for the U.N.

In her previous life, Aida was a teacher. Her husband, Nihad (Izudin Bajrovic), was the principal of the local high school. At one especially tense moment, she and a Serb soldier exchange polite greetings: he’s a former student, who sends regards to Aida’s sons, Hamdija (Boris Ler) and Sejo (Dino Bajrovic). That encounter is one of several reminders of the prewar normal, when Serbs and Muslims lived side by side and Aida and her family pursued an uneventful middle-class existence. A flashback shows her participating in a whimsical pageant devoted to “Eastern Bosnia’s best hairstyle.”

Now, she runs an increasingly desperate gantlet of contradictory demands. Her U.N. identification badge affords her some protection, which she tries to extend to her husband and children. She persuades Nihad to volunteer as a civilian delegate alongside the U.N. commander in farcical negotiations with Mladic, and uses her access to restricted areas of the base to find hiding places for Sejo and Hamdija.

In her official capacity, Aida dutifully translates Serbian lies and U.N. equivocations, a role that becomes both horrific and absurd. She must convey to the panicked masses at the base — some of them her friends and neighbors — reassurances that she knows to be false. Amid the promises of safety, she can see clearly what is about to happen.

Duricic’s performance is somehow both charismatic and self-effacing. Aida is tenacious and resourceful, and also terrified and overwhelmed by circumstances. The story she is caught up in moves swiftly and relentlessly, but sometimes nothing seems to move at all. The victims-in-waiting are trapped. Their ostensible protectors are paralyzed, and the predators are in no particular hurry. Who can stop them?

There is relentless, dread-fueled suspense here, and a kind of procedural efficiency that reminds me of Paul Greengrass’s fact-based films, like “Bloody Sunday” and “United 93.” The rigorous honesty of “Quo Vadis, Aida?” is harrowing, partly because it subverts many of the expectations that quietly attach themselves to movies about historical trauma. We often watch them not to be confronted with the cruelty of history, but to be comforted with redemptive tales of resistance, resilience and heroism.

Aida may have some of those qualities, but her brave attempts to escape only emphasize how trapped she really is. The title asks where she is going. The available answers are grim. If she can save herself, can she also save her family? And if so, what about the thousands of others whose lives are in peril?

Her situation is dramatized with exquisite empathy. Pity isn’t the only emotion in play; it does battle with shame and disgust. The failure of the U.N. is almost as appalling as Mladic’s viciousness. The rule-bound, well-meaning Dutch officers in charge of the base become the general’s hostages and then his accomplices. The massacre was a war crime supervised by peacekeepers — a failure of institutional resolve, of humanity, of civilization.

Eventually, Mladic was tried in The Hague and sentenced to life in prison. The final act of “Quo Vadis, Aida,” Bosnia and Herzegovina’s official Oscar entry, makes clear that many other perpetrators escaped with impunity. The war ended, and some version of normalcy returned, but Zbanic takes no consolation in the banal observation that life goes on. It’s true that time passes, that memory fades, that history is a record of mercy as well as of savagery. But it’s also true — as this unforgettable film insists — that loss is permanent and unanswerable.

Quo Vadis, Aida?
Not rated. In Bosnian, English and Dutch, with subtitles. Running time: 1 hour 41 minutes. Watch through Angelika’s virtual cinema.