Tales from the Crypt (1989)

S4E8 Maniac At Large

A timid library clerk becomes fixated on a serial killer, convinced she might be his next target. She suspects her boss, the security guard, and a library patron of being the murderer. However, during a late-night shift, a shocking revelation unfolds: she is, in fact, the killer, having eliminated those she believed were threats to her. As the truth unravels, the lines between victim and perpetrator blur in a chilling twist.