It was in the opinion of many people that serial killers were absolute lunatics or unhinged, cold-blooded thugs.
The fact was that it wasn't an accurate representation. Serial killers weren't all the same. Studies have shown that a number of them come in the form of highly educated idealists who have a high sense of morality, even willing to sacrifice themselves in pursuit of the truth they so desperately sought.
They often came as good-looking, well-dressed, and well-spoken individuals with stable careers and closed interpersonal relationships. As for how they ended up being serial killers, the reasons varied from one individual to another.
The Federal Bureau of Investigation defines a serial killer as a person who has murdered three or more people, with a cooldown period between the crimes. Unlike mass killers, they would carry out massacres in one place in a short period, or spree-killers who murdered in a frenzy.