Demon in My View by Ruth Rendell (aka Barbara Vine)
Arthur Johnson's loneliness has perverted his desire for love and respect into a carefully controlled tendency for violence. One floor below him, a scholar finishing his thesis on psychopathic personalities is about to stumble upon one of Johnson's many secrets. He is also called Johnson and this will give unexpected complications.

We see the story from both their points of view so it is interesting to see how they interpret the same situations. Rendell writes so well and leaves you wanting more. I'm enjoying going back through her older works.