Memory is fragile, and often changes over time.

In the new feature documentary Out of Thin Air, which will enjoy a world premiere at Hot Docs Monday (May 1), UK director Dylan Howitt explores that theme through the most infamous murder cases in Iceland’s history. Two unrelated men, Gudmundur Einarsson and Geirfinnur Einarsson, disappeared in 1974 within ten months of one another and their bodies were never found.

Gudmundur was the first to disappear on a cold, snowy night in January. The 18-year old casual laborer never made it back home near the town of Hafnarfjordur, south of Reykjavik, from a party he was attending. Then, in November, while at home with his family, 32-year old Geirfinnur received a phone call that took him out to a harbor cafe in Keflavik. He parked his car nearby, got out and never returned. 

The murders set off a national crisis in the small, remote country that, until then, was unfamiliar with violence of such magnitude.

“The word ‘Geirfinnur’, who was one the people who went missing, has become part of common folklore. If you lost something or go into an undiscovered room it’s like ‘Oh, will you find Gerfinnur there?’ Everybody has an opinion about it,” Andy Glynne, a clinical psychologist and executive producer of Out of Thin Air, tells realscreen. 

Six people – five men and one woman – were eventually arrested and sent to prison for the crime, to which they confessed. One of the men received the longest sentence in Icelandic history – life plus one year.

More recently, the case has come back to the forefront of discussion when the murder cases were reopened in 2015 following a report by a task force appointed by the country’s Ministry of the Interior to review the cases.

In February 2017, the ministry’s committee said the murder cases would be reheard by the Supreme Court.  

Glynne was instantly gripped by the murders when he first read about them on a BBC website.

With its frigid, rocky countryside and small population, Iceland represents a bygone era where everyone knows everyone, he says, adding, “It’s a country with a small-town ‘Fargo’ sensibility.”

But it wasn’t just the true crime aspect that grabbed his attention: The story, he says, is “fascinating in itself — psychology of memory. What is real and what isn’t real?”

It proved a difficult film to make, in part because the story is so dense. With the trend towards serialized docs like Netflix’s Making a Murderer, Glynne thought this project could easily morph into a 10-part series. But, as a feature doc, the challenge became distilling all the twists and turns into a single narrative.

“What we were trying to do is not make this into a miscarriage-of-justice story. It wasn’t a forensic, investigative, journalistic film. We’re not trying to come to conclusions of who did what, guilty or not guilty. What we really wanted it about was memory and the fallibility of memory,” says Glynne.

When interviewing people — 24 in all — the team strove to stay neutral on people’s guilt or innocence, which Glynne says helped them maintain good relationships with the subjects because they didn’t have an agenda.

“I think creatively it helped us keep focus of what the film was about; with such a dense subject matter its easy to get lost in the detail.”

Glynne says the starkly beautiful landscape of Iceland also plays a prominent role of the film – almost a character in itself. To that end, cinematographer Bergsteinn Bjorgulfsson was brought on board to help craft the narrative tone through sweeping shots of the landscape.

Music is also integral, adding a subtle, melancholic vibe to the film. Looking for a Nordic minimalist aesthetic, Glynne turned to BAFTA-award winning instrumentalist and producer Ólafur Arnalds, who also did the score and end credits for ITV’s Broadchurch in 2013. 

This time, Glynne says, “We opted for a very subtle piano effect and strings. We scored it all and recorded it live.”

The single biggest production issue on the 12-month shoot was not something anyone anticipated in Iceland, however: Waiting for the snow.

“This winter was one of the warmest in Iceland’s history in the past 200 years,” says Glynne of the frustration.

• Out of Thin Air world premieres May 1 at 8:45 p.m. ET/PT at the Scotiabank Theater