Revisiting the blood-soaked conflicts that followed the breakup of Yugoslavia in 1991, Viktor Portel’s harrowing documentary follows Vladimír Dzuro, a Czech investigator committed to bringing war criminals to justice. Drawing from Dzuro’s bestselling book The Investigator: Demons of the Balkan War, the film primarily focuses on the atrocities committed by Serbian forces; as Dzuro returns to sites of torture and death, his encounters with the survivors as well as supporters of the perpetrators are at once riveting and heartbreaking.

The Vukovar massacre, one of the most infamous incidents of the war, is recounted in eye-opening detail. In 1991, in the final days of a battle between the Croatian National Guard and the Serb-controlled Yugoslav People’s Army (JNA) during the Croatian war of independence, the latter vetoed an agreement to evacuate the Vukovar hospital and turned it over to Serbian paramilitaries. In the end, nearly 300 people were executed in cold blood and dumped in mass graves. In 1996, Dzuro was a part of a mission to exhume the victims. Flickering archival footage of the campaign shows piles of bodies laid beneath the ground, a chilling visual manifestation of how history can be buried and erased. In contrast with the lo-fi quality of these newsreels, contemporary footage of Dzuro has the stylisation of a crime thriller. The look creates a gripping atmosphere, even if it also occasionally verges on overdramatisation, which the film’s already shocking true stories don’t necessarily need.

Working with the International Criminal Tribunal for the former Yugoslavia (ICTY), Dzuro played a pivotal part in bringing the crimes of former Serbian president Slobodan Milošević, infamous paramilitary leader Arkan and others to light. Yet, the film also suggests that true justice is an elusive ideal, one that can’t merely be satisfied by a system of trials and sentences. Against institutional attempts to distort and efface state-sanctioned atrocities, the act of collecting evidence is only the beginning.

• The Investigator is on True Story from 28 June.