Predicting who's at risk for violence isn't easy

CHICAGO (AP) — When horrible crimes happen like the Connecticut school shootings, people figure there surely were hints of impending violence. But experts say predicting who will be the next mass shooter is virtually impossible. That's partly because as commonplace as these calamities seem, they are relatively rare crimes.

Experts say mass shooters sometimes plan their clothing and prepare by target practicing, or voice threats. But most people who make violent threats never act on them.