An intrepid expert with dozens of books to his name, Stéphane Bourgoin was a bestselling author, famous in France for having interviewed more than 70 notorious murderers. Then an anonymous collective began to investigate his past

One night in the early 1990s, at a dinner party at his home in Paris, Stéphane Bourgoin, an author and bookseller then of no particular renown, began to hold forth on the matter of serial killing. The topic was, at the time, quite novel. As a cultural trope, the string of mysterious homicides had of course been a fixture around the world since at least the time of Jack the Ripper, and the French more specifically had been acquainted with the idea since as early as the 15th century, when the nobleman Gilles de Rais was found to have kidnapped, tortured and ritualistically murdered nearly 150 young children. But these people had not been understood as “serial killers”. That phrase, and the notion that such criminals were a breed apart, impelled by a special, sexualised depravity, really entered into the popular imagination only in the 1970s, and then mostly in the US, where the FBI had established a unit of so-called “profilers” to catch them. The serial killer was not yet a cultural vogue in France, much less the cliche it was already becoming elsewhere. Bourgoin’s guests were barely familiar with the concept at all. They listened, as millions of other French-speakers would listen in the decades to come, horrified, nauseated and rapt.

Bourgoin told his invitees of the FBI programme, of the traits of the typical killer, and of some of the more awful American specimens. “We were utterly captivated,” Carol Kehringer, who was among Bourgoin’s guests that night, recalled recently. Kehringer was then in her 20s, starting out as a television producer. “I started asking him all sorts of questions,” she said, “and the more he spoke, the more I thought to myself: ‘We’ve got to do a film!’”