The first weekend of Millennium Docs Against Gravity – the prestigious international film festival in Poland – is underway after opening with Closure, the new film directed by Warsaw native Michał Marczak.

The wrenching documentary about a father’s desperate search for his missing teenage son won the Golden Alexander at the Thessaloniki International Documentary Festival in Greece in March and premiered in World Cinema Documentary Competition at Sundance.

Marczak’s journey to make the film began as he spent time on the Vistula River in Warsaw. While on a raft with his family – the director was scouting locations for a fiction project — he noticed a man plying the waters intently in a boat. After engaging him in conversation, Marczak learned the man, named Daniel, was looking for his son Chris who had last been seen standing on the Warsaw Bridge overlooking the river.

“A rotating CCTV camera caught [Chris] there standing for 20 minutes. And as it swung back around, we don’t know if he jumped or made it off the bridge and possibly escaped,” Marczak told Deadline’s Doc Talk podcast. “The father decided to search the river by himself. He built this custom-made boat outfitted with cameras, sonars, drones to probe the murky waters. So, it’s a ‘an old man in the sea’ type of a story, a Fitzcarraldo-type character, fighting against all odds to find the truth about what happened.”

Marczak spent many months with Daniel as he continued his search, sometimes the two of them camping along the river.

“Many times, it was just easier to sleep on these islands or banks and so that you don’t waste time and that most of the time goes for the search,” he recalled. “After [searching] for hours and you sit down at night, exhausted, by the campfire, all these thoughts come to you — about what could I be doing better, or how could I navigate the challenges of raising my now two sons in this world? And where, as a society, we have gone wrong… Totally desolate, empty nature yields these kinds of more metaphysical conversations. So, we would just sit and contemplate our lives. And I would ask him for advice. He would ask me, and that’s how we became close to each other.”

Without knowing if his son jumped to his death or perhaps left the bridge and is still alive somewhere, Daniel cannot find closure, nor can his wife. Daniel keeps searching month upon month, unable to give up on his son, even as his father counsels against continuing what could be considered an obsession.

“It’s a psychological film about the effects of that situation on the family and on Daniel,” Marczak notes, adding, “and on other families as well.” Other families whose loved ones have gone missing after hurling themselves from the bridge.

Introducing the film at the Multikino Złote Tarasy venue in Warsaw, MDAG Artistic Director Karol Piekarczyk said Closure had helped him deal with grief in his own life. The impact of Closure has been similarly profound for many viewers. In Thessaloniki, Marczak told us about a voicemail he received from a person who had seen the documentary.

“He said, ‘Listen, I’ve had some bad days. I’ve had really deep, dark thoughts. But after I saw your movie, I know that I’m never, ever going to commit suicide,’” the director recalled. “And I cried when I heard that message.”

At the festival in Greece, Marczak told us the film came together at almost lightning speed by documentary standards.

“We did this movie in 14 months from the moment we met the protagonist and we shot for a year,” Marczak explained. “We were super-fast editing as we went, just really trying to stretch our resources and to get this movie out.”

In addition to Sundance and Thessaloniki, Closure has screened at True/False in Columbia, MO and will screen next month at Sheffield DocFest in the UK and at the Sydney Film Festival in Australia.