Can you look at a person's face and tell if they have a psychological problem?

During my 44 years as a police officer, I have confronted some people that, to me, had psychological problems. I determined this from some of the facial expressions they presented, when asked questions by me. We are not doctors, but experience can educate you in so many ways. Some people would possess a far away look and some would stare you down, most of the time.

Question: have you ever encountered a person that you suspected has a psychological problem, just by the look on their face?