Recently, I read a book by Robert Hare, "Without Conscience." He is a psychologist that specializes in the field of psychopaths. This book was easy to read and lists the common characteristics of psychopaths. Surprisingly, the author estimated 2-3 million psychopaths in North America alone and the book was written ten years ago.
They have no remorse, feel nothing for their victims, commit fraud, lie a lot, no fear, glib, and being caught in a lie doesn't faze them.
This book makes me wonder about Willy the Zipper and Hitlery...