Law & Order: Special Victims Unit 5x23

Bound

A nurse, whose brother owns the home-nursing company she works for, takes her childhood abandonment frustrations of her mother out on the rich elderly women the company cares for, leaving the detectives to believe they have a money-hungry serial killer on the loose. The detectives know the nurse has committed the murders of what they thought was six people, but they cannot prove it, that is untill Benson and Stabler do a little roleplaying and get the nurse to confess that she has killed numerous elderly women and framed the murders on her brother as a way to get back at her mother and brother.