Until one month ago, the prolific true-crime author and documentarist Stéphane Bourgoin was France’s foremost expert on serial killers. Dressed in kitschy flowered shirts and flashy shoes, with a gift for dramatic rehashing and a glee for gore, Bourgoin was like the thirsty, gnomish love child of Jimmy Buffett and David S. Pumpkins.

With obsessive insight and purportedly intimate firsthand knowledge of famous criminals, but no actual degree or verifiable expertise, he has authored around 40 books, mostly in the true-crime genre, hosted conferences, pontificated on prestigious sound stages, and put his name to a series of comics on famous killers. He claimed to have interviewed 77 serial killers, among them Charles Manson. For years Bourgoin said he knew the identity of the killer of Elizabeth Short, better known as the Black Dahlia, whose 1947 murder gripped Hollywood for decades. The French public ate it up for more than three decades.