Twisted Nerve (1968)

Twisted Nerve (1968) Martin is a troubled young man. With a mother who insists on treating him like a child, a stepfather who can't wait to see the back of him, and a brother with Down's Syndrome shut away in an institution, is it any wonder he retreats into an alternate personality - that of six-year-old Georgie? It is Georgie who befriends Susan Harper, but friendship soon turns into obsession. When Susan begins to distance herself, something inside Georgie snaps and he embarks on a killing spree, with Susan as the next target.