Why serial killers kill

There have been 220,000 unsolved murders in the U.S. since 1980. Are serial killers to blame? Here's everything you need to know:How many serial killers are there?Since 1900, there have been 3,000 identified American serial killers who've collectively killed nearly 10,000 people, says Dr. Michael Aamodt, who oversees the Radford University/Florida Gulf Coast University Serial Killer Database. The FBI defines a serial killer as someone who kills two or more people in separate events. About 32 per