YMMV / The X-Files S04 E10 "Paper Hearts"

• Complete Monster: John Lee Roche is a sociopathic pedophile who gets the parents' trust by pretending to be a nice guy and manipulating them, but at night, he kidnaps their children and put them through torture, before killing them. When he's arrested, he still manages to do his hobby, manipulating Agent Mulder into thinking that he kidnapped Mulder's little-sister Samantha who went missing. When he escapes prison, he almost immediately kidnaps yet another girl and holds her hostage, and when Mulder finds him, Roche tries killing her.