Director Fabrice du Welz was 20 years old when the Dutroux case exploded, and it has a profound impact on him, as he realized the real world was much more chaotic and scary that he previously thought. He had always wanted to make a movie about it, but couldn't find the right angle. It's only after watching Once Upon a Time In... Hollywood (2019) and how Quentin Tarantino managed to address the terrible story that is the Sharon Tate murder that it clicked for him; he would make a fictional movie that would border on the alternate reality, where there would be a sense of justice compared to the parody of justice the victims' families got.
The story is freely inspired by the infamous Dutroux case, named after Marc Dutroux, who kidnapped, sequestered, raped and killed several girls on the 90s in Belgium. The rivalries between law enforcement agencies and the general judicial dysfunctions resulted in a botched police investigation and a lenient prosecution, which in turn caused widespread outrage in Belgium, culminating in a march joined by more than 300,000 people and a major law enforcement reform in the country.
The movie was mostly shot in and around Charleroi, Belgium, the setting of the Dutroux case, and the movie highlights the Sicilian community in Charleroi that originally came to work in the mines. Several minor roles were also cast with locals.
The title comes from Les Chants de Maldoror (The Songs of Maldoror), a French poetic novel written in the 19th century by the Comte de Lautréamont. According to the director, the novel talks about exploring the propagation of evil, its impunity and its consequences, like the movie, even though it is set in modern times.
When Charles Hinkel (Laurent Lucas) visits Remacle (Mélanie Doutey), he looks at a picture of her with her husband, who is the actor Benoît Poelvoorde (thanked in the end credits).