Question about mental health?

I have a friend who has really screwed up eyes. When he talks to you it's like he stares right through you. I will also add that he can be quite a sadist (someone who enjoys seeing other people experience pain and suffering). I would even go so far as to say that his look can rival that of Hitler. I've already made up my mind that he has underlying mental problems and I can't help but notice some of the most evil people in history (Hitler, Ted Bundy, other serial killers and rapists) all have the same look in their eyes. Is their some kind of link between mental instability and this look in the eyes. You could describe it as lifeless, emotionless, and even evil. It's just so odd.