Even the most banal phrases have their uses, and when it came to Bart Layton's documentary “The Imposter” earlier this year, it's easy to understand why so many critics reached for that fusty standby: “The truth is stranger than fiction.” Then again, “The Imposter” – one of 15 shortlisted films vying for an Oscar nod in the Best Documentary Feature category – tells a story that is stranger even than most truths.

Centered on the charismatic, frightening figure of Frédéric Bourdin a shapeshifting con artist and serial identity thief who claim to have masqueraded as over 500 people in his lifetime, the film peels back the covers on the Frenchman's most infamous and improbable stunt. In 1997, aged 23, he seemingly duped a Texan family into accepting him as their teenaged son who had gone missing three years previously – despite not sharing his accent, appearance or even eye color. Turning up in Spain and claiming to have been kidnapped by a military-run child prostitution ring, Bourdin sold his outlandish tale not only to the Barclay family but to the US authorities, and maintained the charade for five months before the FBI caught wise.

It's irresistible material for any movie – non-fiction or otherwise – and it's easy to see why Layton, a young, London-born documentarian previously best known for the UK television series “Banged Up Abroad,” was drawn to it for his first feature film. Layton first encountered the story by chance, while flipping through a magazine at a friend's house in Spain; he knew he wanted to do something with it, but didn't quite know what.

“I kind of made a note and didn't find the note again for some time,” he says. “When I got back to it, I felt pretty sure it must have been made into a film – either as a documentary or as a fictionalized version – and was astonished to find that it hadn't.”

He's speaking over the phone from Los Angeles, where he's been put to hard work on the Oscar campaign trail – not that he's had much of a moment to breathe since the film's buzz-making debut at the Sundance Film Festival 11 months ago. Even this interview is our second: in the summer, I hosted a Channel 4 Q&A with the director in our mutual hometown, and if he's grown at all weary of discussing the film in the intervening months, he doesn't sound it.

After reading up further on Bourdin's story, notably via David Grann's extensive 2008 profile in The New Yorker, Layton got in touch directly with the so-called Chameleon through his Bourdin's YouTube account, and invited him to London to discuss a potential collaboration. “At that point,” Layton says, “I didn't exactly know what the film would be about – whether it would just be about him, or use his story as a way into something bigger. Which is what we ended up doing.” The attention-grabbing result is an unusual hybrid documentary, remarkably securing the on-camera participation of both Bourdin and the Barclays, but blending their testimonies with stylized, suspenseful dramatizations that evoke film noir more than cinema vérité.

“I never really considered making it as a narrative film,” he explains. “But that's such a strange term in the first place: aren't all documentaries narrative?” That's just as well, since after Layton began work on “The Imposter,” a little-seen, faintly fictionalized film of the story, with a cast including Famke Janssen and Ellen Barkin, was released in 2010; it's not much of a match for Layton's take.

“I felt all along that it's such an unusual and extraordinary story that if you fictionalized it at all, it would seem completely preposterous,” he says. “You wouldn't believe it. Listening to the people involved telling their stories, it did feel at times like you were listening to the plot of a Coen Brothers film, and I wanted the film I made to have a foot in both camps. Clearly it's a documentary, with real people, and we were journalistically rigorous about keeping to the details of the case as we understood them. But it was always my intention for the film to play to an audience that might not normally go to see a documentary in the cinema.”

Layton, therefore, has no issue with people describing his film as a thriller – a fragile sense of mystery was key to the filmmaking process. “While making it that I felt we were inside our own detective novel in some ways,” he laughs. “We ourselves experienced a lot of twists and turns along the way. You'd have a conversation one day with a member of the Barclay family and come away convinced of one conclusion, and the next day talk to the FBI, and come away equally convinced of the opposite. So while making the film, our sympathies were swinging to different extremes, and that was something that I really tried to reflect in the way the story was told.”

The audience, too, will feel torn between Bourdin's cool, calm, vaguely amused-sounding retelling of events and the more stricken accounts of various members of the Barclay family as they struggle to explain just how they were so absurdly fooled. Between them, it's all too easy to believe the more sinister theories that suggest the family played along with the deception to cover the nastier truth about their son's disappearance, but this slippery even-handed film never takes sides. Getting the perspectives of all involved parties is essential in this regard, but it wasn't easy to do.

Guy Lodge is a South African-born critic and sometime screenwriter. In addition to his work at In Contention, he is a freelance contributor to Variety, Time Out, Empire and The Guardian. He lives well beyond his means in London.