This is a fairly straight-forward account of the crimes of Joseph Vacher. "Vacher" and "Bouvier" both mean "cowherd" in French. The names of many of the characters - like Lacassagne - have not been changed.
Philippe Noiret and Isabelle Huppert later co-starred in Clean Slate (1981), also directed by Bertrand Tavernier.
Based on a true story.