Inspired by a rumour about the well-liked young Saloth Sar losing the love of his life, Swedish novelist Peter Fröberg Idling came up with a fanciful creation story for Pol Pot.

Did Pol Pot turn to fanaticism after Sam Rainsy’s father swooped up the love of his life in 1955? It may sound like the stuff of tabloids, but Swedish author and journalist Peter Fröberg Idling found the idea just plausible enough to make it the plot of his debut fiction novel Song for an Approaching Storm.

“If you have a puzzle, and some pieces are missing, you gather as much as you can with the existing pieces and you imagine what the rest would be like,” Idling said in a Skype interview from Stockholm earlier this week.

The plot of Song for an Approaching Storm focuses on the month preceding Cambodia’s first post-independence election, which saw Prince Norodom Sihanouk’s Sangkum party win all 91 seats in parliament. Saloth Sar, a well-liked school teacher many years before he changed his name to Pol Pot, works as the secretary for his mentor, opposition campaigner Keng Vannsak.

He is also an operative for “the Organisation”, an underground communist network largely comprised of radicalised alumni from French universities. A devoted Marxist who found solidarity among other radicals from around the French Empire, the only thing he cares more for is his girlfriend Somaly, a former beauty queen with royal blood.

But it is not just Sar who has feelings for Somaly. Sihanouk’s right-hand man Sam Sary, who is torn between his liberal democratic leanings and loyalty to Sihanouk’s repressive government, woos her with promises of a better life as his mistress in Europe’s high society. Sar is left heartbroken and forever loathing of the bourgeois world for which Somaly left him.

Fanciful as the story sounds, it was related to Idling by the real-life Vannsak in an interview conducted for the author’s first book.

Vannsak told Idling that a woman named Son Maly, upon whom the character Somaly was based, was among the mistresses who Sary brought to London with him after being appointed ambassador in 1958. Sary’s mistresses became public knowledge after one of them appeared in a London hospital alleging that he beat her. But Sam Rainsy – who wrote in his biography that it was, in fact, Sary’s jealous wife who committed the assault – told Idling in a subsequent interview that his father did not keep a mistress matching Son Maly’s description. Idling concluded that Vannsak, who died before he could be confronted about the discrepancy, was an unreliable source.

Idling said: “Keng Vannsak’s story is contradictory and somewhat confused. Which is peculiar, as he was a first-hand witness who supposedly knew all the people involved quite well.”

With the rumour apparently having no grounding in reality, Idling decided Vannsak’s story would work best as a fictional narrative. Although Song for an Approaching Storm makes extensive use of real-life figures, the author made no pretensions that the plot is historically accurate.

“I think that if you have documentary material and you just add one single drop of fiction, then it will contaminate the whole material and everything becomes fiction,” he said, adding that he thinks it is more likely Pol Pot became radicalised while living in the dense jungles of Cambodia’s northeast in the 1960s.

Despite the novel’s lack of historical authenticity, Idling took great pains to create a believable Pol Pot. Doing so, he said, required writing a character he could sympathise with.

“As an author you always sympathise with your main characters – it would be impossible to write a book where you don’t sympathise with them.”

Strange as it may seem to have a sympathetic Pol Pot as a novel’s protagonist, Idling added that contemporary sources from the 1950s describe Saloth Sar as a likeable person.

It took many months of constant rewrites before he found the proper voice for the character. He finally tried writing the character in the second person and found that it worked.

“It was almost out of frustration that I started to write in the second person, and suddenly I realised it was the way to do it. It enabled me to recreate the atmosphere that I wanted for that part.”

Idling’s fascination with Pol Pot’s persona stretches all the way back to his childhood. He said that his mother, who was active in the anti-war leftist movement of 1970s Sweden, was initially sympathetic to the Khmer Rouge’s avowed anti-imperialist struggle.

“My first childhood memory that I can actually date is the 17th of April 1975, when there was a celebration in Stockholm when Phnom Penh had been, so to speak, ‘liberated’ by the Khmer Rouge,” he said.

A few years later, when Idling was still a child, he stumbled upon articles and photographs detailing the Khmer Rouge atrocities that were unveiled after the Vietnamese invasion.

“I remember all these images from the Killing Fields with the craniums, the piles of bones and all that. Of course it made quite a strong impression on someone who was six or seven.”

But it was not until Idling took a job with a Cambodian NGO in 2001 that he began his professional examination of Pol Pot. His first book on the subject, the Swedish language Pol Pot’s Smile, was a literary nonfiction account of a group of radical Swedes who had a friendly dinner with Pol Pot in the summer of 1978 on a delegation to Democratic Kampuchea. Idling said that the members of the trip he interviewed all left with favourable impressions. Only one admitted to Idling that he had been wrong, with two of them defending Pol Pot decades after the truth emerged.

“The worst case, one of them said, was that Pol Pot had been misunderstood – what we think we know about Democratic Kampuchea is just a propaganda myth, and he actually said that if Pol Pot had been allowed to continue his reforms, Cambodia would be a much better place today.”

But most of the old supporters in Sweden admit they were wrong, and Idling said that growing up among them helped shape his views.

“When you have the idea of a utopia, my impression is that the road to that utopia will always go through hell,” he said.

By getting into the mind of Pol Pot, said Idling, his book serves to highlight uncomfortable common ground between an ordinary reader and a genocidal dictator guilty of murdering hundreds of thousands.

“If we don’t recognise all that we have in common, all the similarities, we will certainly make the same mistakes again further down the road.”