I think this is the root of it. Before the advent of mass media, you would hear about crimes if those crimes happened to people you personally know, but probably not otherwise. Rare crimes were rarely heard about and therefore people had an intuitive understanding that those crimes were rare. Mass media changed all of this. The most rare sort of crime is the most newsworthy because novelty sells newspapers. So the media has people fixated, worrying, about very rare sorts of crimes and this has made the general population much more irrational about rare crimes than it ever was before. Journalists may sometimes say that their job is to inform the public, but very often they induce a perception of reality that is less accurate than what people would have formed on their own with no journalist around to make a huge deal out of freak rare occurrences.