For years, documentary-maker Vanessa Engle has been on the trail of a notorious swindler who escaped from prison and disappeared into thin air. Then one day, the phone rang ...

You probably haven’t heard of Michel Cohen. Do a search and you get Michael Cohen, the Trump fixer who went to jail. Wrong one. Though this one did go to jail, too. He’s French, born in 1953 on an estate in a poor suburb of Paris and his first job was to sell the Encyclopedia Britannica door-to-door, which he was very good at.

Cohen later went to the US and started selling French paté, then prints. He got into the art world, became a dealer, sold Picassos, Monets, Chagalls. For a while he lived the dream, drove fast cars, had a house in Malibu with his German wife and two kids, a chef, horses, everything. He got into the options market. That didn’t go so well, so he got into debt. Cohen started to put loans and artworks that weren’t his into the market; the hole got bigger and bigger. In the end he disappeared, having swindled the New York art world out of $50m.

That was in 2001. Vanessa Engle, the documentary maker (The Funeral Murders, The Cult Next Door, Women, Jews, Lefties, loads of other brilliant stuff) was making arts documentaries at the time. She clocked the story as one to keep an eye on.

And she did … for 17 years. “Nobody knew where he had gone; he had just vanished with his wife and kids,” she says. “I thought it was an interesting story, but I didn’t have a way in. The art world is very secretive, they don’t like to talk, especially if they have just been ripped off to the tune of many millions. It’s a world built on trust. Clients are not going to want to know a dealer of a gallery that could so easily be defrauded.”

We’re in a north London pub, and Engle is telling me about her manhunt: the search for Cohen. “I’ve searched his name online every two or three months for 17 years.”

Facebook Twitter Pinterest ‘He just vanished’ ... Cohen. Photograph: BBC/Top Hat/Michel Cohen

The first hit came in 2003: a small story in the US press. Cohen had been arrested, by Interpol, in Rio de Janeiro; he was in jail in Brazil. “I thought OK, now’s my chance, maybe the Brazilian authorities will let me into the prison, I can get the whole story, it’s going to happen,” says Engle, reliving the excitement.

She was on another project, but there was no hurry because he would be in prison for a long time. Then, later that year, she searched again and … he had escaped! The story just got better – Papillon meets The Goldfinch meets The Great Train Robbery. But it had also gone cold. “I thought: oh, I’ve missed it.”

The trail stayed cold for years, although Engle never forgot about Cohen. In 2017 she spoke to a commissioning editor at the BBC. She didn’t think she would find him, didn’t even know if he was alive, but she could talk to his friends, and people in the art world.

“I’ve often said I should have been a policeman because what we do is the same,” she says. “We gather clues to put together a plausible story, and find witnesses who can testify to that story.”

Yet Engle argues she’s not really the detective in this story. “I’m good at getting people on board, mapping the story, but if it was not for Billie …” Billie is Billie Shepherd, the producer Engle hired because she worked on Who Do You Think You Are? and knows how to find people. “You don’t want to fall out with Billie,” says Engle. “She will track you down.”

They made a timeline of transactions, paintings, swindles and people; it ran to more than 100 pages. They called in legal documents from the US and Brazil, sometimes getting people to go to court and photocopy them.

Once they had names and addresses, they made a big drawing: Cohen in the middle, then his inner circle of family and close friends (people such as Richard Roy, who plays a big part in the film), followed by an outer circle of those he had done business with or ripped off.

Then Engle wrote letters to them. She had heard rumours there were people who wanted to have Cohen assassinated. “There are people in the art world who have mafia connections, laundering money,” says Engle. “It’s actually quite a dirty business. In the end, I was convinced there are people who would know where to get a hitman.” Or he might just be dead; he would be in his mid-60s.

Facebook Twitter Pinterest Vanessa Engle: ‘I should have been a policeman.’ Photograph: Johann Perry/BBC/Top Hat

She concentrated on the outer circle first, fearful that someone near Cohen would tip him off and cause him to run. They got some hits: old acquaintances who agreed to talk, dealers, just about enough to make a film. “Then we thought, we’ve got nothing to lose, and pressed go on that last lot of letters, including ones we hoped might get to his family and – maybe – him.”

Engle waited. There was no response from Cohen’s sister, but they got Roy, Cohen’s friend and business partner, who had gone to the US with him and set up the paté business. “When we got him, me and Billie were just screaming,” says Engle.

Then, one day, Engle was at home when the phone rang. “This woman said: ‘My name is blablabla’ [she doesn’t want me to know the woman’s name]. I was distracted, I didn’t know if it was the wrong number, or someone asking if I was satisfied with my gas supply,” she recalls. “I can be slightly brusque, so I said: ‘Sorry, who is this?’”

It was Cohen’s wife, who had also gone to Brazil with the two kids, had a third there, then had a really tough time after he was arrested. She was going to be able to fill in the missing pieces, perhaps even lead Engle to the man himself.

Cohen’s wife was very nervous. She said she couldn’t really talk on the phone, didn’t say anything about where Cohen was or whether he was still alive, but did agree to meet in a cafe. Not in London, but a different country – and Engle was to come alone. The BBC weren’t happy about that, so a colleague went as well, pretending not to be there, tracking Engle’s phone.

Mrs Cohen, it turns out, was “lovely, sweet and warm”. She talked for hours. Now, would she do it on camera? Absolutely not. Uh oh. It is a shame, but not the end of the world, because ... well, it’s in the film.

Which is fabulous; a stonkingly good romp. Not a million miles away from the Netflix Fyre festival documentary, but with more personality, motifs and metaphors running through it. “And we got the guy!” says Engle. “There has been a whole spate of these films where you have a central protagonist who’s done something really wrong, but it’s very rare to get the guy.”

Oops, spoiler alert. Actually, not such a spoiler: he’s there, right at the beginning of the film. He was there in that cafe, too. “A small man shuffled up to the table, unshaven, his hair was quite long, wearing a scruffy sweatshirt,” says Engle. “I thought: is that the guy I’ve been looking for for 17 years?” And it was.

• The $50m Art Swindle is on BBC Two on 23 September 2019 at 9pm.