The movie started out good and then the end ruined it. It doesn’t show who the killer is or why he is doing it. It took a while to even come up with a theory of who it is and why.
Theory: the killer is the plumber. If you compare the scene of the Plummer talking to the mom and the scene where the killer is taking out Logan’s contacts you can see a few similarities. Although the contacts scene was blurry you can see a few similarities in the plumbers hands and his double chin. The Plummer is the husband of Martha and Martha has Alzheimer’s or dementia. The reason he is doing it is there is no specific reason because he is a serial killer.