“The term serial killer designates a predator who murders repeatedly and with a certain general periodicity. And after each crime, there is a “cooling-off” period. If the killer stops without being caught, it is almost always for one of three reasons: He has died; he has been arrested for an unrelated crime and is in prison; or he hasn’t actually stopped, but has merely moved to another area and law enforcement has not connected his new crimes with the older ones.”