Into the Murdering Mind - S7.E14

A family is violently murdered in their own home. The man arrested is the son and brother of the family members. He is a schizophrenic who blames everything on ‘The Beast', an alter ego inside his head who can take him over if he stops taking his medication. Quincy thinks, after talking with the DA, that he could be making it all up to get off on an insanity plea and tries to prove his theory.