Scandinavian crime dramas have been thrilling avid readers, cinema-goers and TV binge-watchers for years. But what about true crime? You perhaps don’t think of notorious serial killers when you think of Nordic countries, but documentary film-maker John Mork leads a three-part series on Peter Mangs, a white supremacist who was 38 when he was arrested for seemingly random murders committed in Malmö.

In Under the Radar: Secrets of a Swedish Serial Killer, the poster prominently features Mangs’ dead-eyed stare and a particularly sinister voiceover opens the series with, “Murder is natural, it’s in nature.” Mork does a good job of establishing the fear that gripped Malmö whilst Mangs was at large but also takes his viewers to Florida, where he believes Mangs embarked on another killing spree, fuelled by racist ideologies and his own troubled past. Split into three episodes – The Secret, The Terrorist and The Musician – the series examines similarities between the crimes he has been convicted of and cold cases that he can clearly be linked to.

Peter’s early life was marred by trauma. His sister died of a drug overdose in 1990 (which, crucially, he blamed on immigrant dealers) and his cold and distant father moved to Florida. “I was raised by yin and yang,” he writes to Mork, “My mother was Bernie Sanders and my father was Adolf Hitler.” But, somewhere along the way, he reunited with his father and the long-haired, vegetarian bass guitarist became a dog-tag wearing skin-head straight out of American History X. He suddenly became obsessed with racist books and ideologies and had access to an alarming number of guns whilst living with his father. “If things had gone differently in Peter’s life,” asks one clinical neuroscientist, “Would he have become a killer?” The documentary doesn’t focus too much on the classic nature versus nurture argument, instead allowing Mork’s encounters with Rudolf (Peter’s father) to do the talking.

All of the scenes in Florida are washed with a yellow grime. It feels less like The Sunshine State and more like a hotbed of decay and barely concealed hostilities. Throughout Mork’s research, he intersperses his reportage with talking heads, most of whom confirm that Mangs displays “classic” psychotic behaviours. He is a weedy, average-looking guy who could not get his music career to take off. “He tried so many things and he failed at every single one of them. The only thing he has success with … was killing people.” Was his lack of greatness fuelling his need to “punish” people?

He also repeatedly feels the need to assert how clever he is, much more so than your average person. He also teases Mork with two songs – one called Under the Radar and another called Cold Telephone – which allegedly map out clues as to who he has killed. Mangs is clearly revelling in his Zodiac killer-esque moment. Hearing segments of these songs sung or played is quite unsettling. Mork’s obsession with unlocking this particular code does make you wonder if he is simply a pawn for Mangs to entertain himself with whilst he remains in prison.

By the final episode, Mangs is linked to around eight other cases in Florida, all of which are entirely possible since passport data confirms he was in the state at the time. Two of his Swedish kills pre-date his Floridian exploits – was he there simply to fine tune his “craft”?  Mork builds the evidence up, bringing in law enforcement, cadaver dogs, ex-FBI, handwriting experts, cold case consultants and behavioural psychologists to analyse the possibility of Mangs being an even more prolific killer than originally thought.

This all leads to the potential for a confrontation between Mork and Mangs – who have been exchanging letters and emails throughout the entire documentary shoot. “What I want you to be careful of is not to believe anything he presents to you on the surface … Any vulnerability you show, he will exploit. John has become his target now,” Dr Sarah Stein warns. Has Mork taken his true crime “obsession” too far? Is he really psychologically prepared to confront a serial killer? Has Peter Mangs simply been dangling the carrot this entire time in a bid to get more attention?

Under the Radar: Secrets of a Swedish Serial Killer ends in a way that will have you begging your TV screen for more. Equal parts frightening and fascinating, this is a well-put-together true crime documentary that seems to be on a genuine path to delivering closure for so many cold case victims and their families.

UNDER THE RADAR – Secrets of a Swedish Serial Killer makes its North American debut on the Viaplay Streaming Service from the 30th July