According to an essay André wrote, Ben's family didn't know anything about the plot of the film. Ben's mother and grandparents thought they were filming raw footage of Ben, and had no idea that the footage was going to be used in a film in which Ben is a serial killer. Ben's mother was shocked to see her son behind bars, when she comes to visit him in prison.
Due to budget problems, it took the filmmakers over a year to complete the film. The company ran out of money several times and shooting had to be postponed until more money could be raised. A lot of friends and family of the filmmakers contributed to the film, both behind and in front of the cameras.
Ben's cocktail "Petit Grégory" is a reference to a murder case in France that involved the killing of the 4-year-old Grégory who was found floating in a river with his hands and legs tied (much like the olive in the cocktail that is tied to a sugar cube). The murder case was covered very thoroughly by the media; a phenomenon that this movie deals with.
The filmmakers were very nervous while shooting the rape scene. The actress who played the rape victim was very supportive of cause of the film, however, and let the filmmakers do their thing. This gave comfort to the crew; especially Rémy Belvaux, who was very shy about his nude scene.