In the 1940s, Bette Davis made a movie called A Stolen Life with Glenn Ford, in which she played twin sisters. Kate was the kind, almost shy one,who met and fell in love with Glenn. Enter Pat, the twin who played around a bit. Pat takes Glenn for herself and marries him. The twins are out sailing together and during a storm Pat is knocked overboard and drowned. As Kate tries to grab her hand, Pat's wedding ring slips off her finger and Kate holds it tight and is knocked backward in the boat. She comes to and finds the ring on her own finger with everyone around calling her Pat, so she decides to play along so she can go home as Glenn's wife because she is still in love with him. It's a wonderful movie.
Much later, possibly in the 60s or later, Bette made another twin movie called Dead Ringer. In this one, the poor sister lures her rich sister to her apartment, kills her and takes her place. 20 years before, the rich girl had stolen the other's boyfriend and married him and they had not seen each other since.
Killer in the Mirror combines parts of both these movies but the twists and turns change it even more. Old movie fans will recognize the Bette Davis movies and begin think it is a remake of one of them until it seems to jump to the other. The name, DeLorca, came from the Dead Ringer movie.
All of these are great movies, but I think Killer in the Mirror is more enjoyable if people have seen the other two first.