Mario Larouche is an arson investigator from Montreal who is killed in Toronto at the beginning of the Season Three episode, "The Human Factor". The character is played by Jean-Pierre Bergeron. Larouche has been involved in an arson ring, covering up evidence of the crimes. When one of his colleagues, Robert McDonagh, suspects his guilt, he murders him. However, McDonagh's girlfriend, Janette, decides on revenge. She tracks him to a motel in Toronto and shoots him. Then she takes from his body the key to a locker where he has hidden evidence that will incriminate other members of the arson ring, most particularly the company ordering the fires.