10 Traits In Which Almost All Serial Killers Have

That is actually very interesting - the distinction between the psychopath (nature) and the anti-social personality disorder (nurture) is something I had not been aware of previously.

Genetics, brain chemistry, psychology and environment are the four factors of human behavior according to the FBI Behavioral Analysis Unit. 

I know a few people that I can fairly certainly describe as narcissists, and I had a chance encounter with an individual who set off every defense monitor I had.  I knew he was dangerous, but talked my way out of the encounter by acting as if I was not in fear, as if I felt empathy for him.  I reported it to the police, they showed me a mugshot which I identified; several years later that mugshot was in the newspaper.  That individual was in custody and charged with the murder of several women.  I about had a heart attack.

One, I didn't fit his victim profile, and this was a chance encounter. Two, I told him that I was expected by family members and was actually running late and needed to leave.  Otherwise, I might have been a victim of opportunity.  But I will always trust the little hairs on the back of my neck - they told me the truth.