Why?

The idea of studying someone's mind to figure out why they turned out the way they are intrigues me. Pin-pointing an event in someone's life that may have "turned them bad" or the way they handled them created a domino effect to become the way they are. Mostly referring to serial killers, and studies done on many of them point to a poor childhood, and events like that. However, I wonder, what was the difference between a serial killer that was abused in their childhood and an executive at a company, married happily, that may have gone through similar occurrences?