FILE - In this Friday, Dec. 14, 2012 file photo, parents leave a staging area after being reunited with their children following a shooting at the Sandy Hook Elementary School in Newtown, Conn., where Adam Lanza opened fatally shot 27 people, including 20 children.  People figure there surely were signs of impending violence. But experts say predicting who will be the next mass shooter is virtually impossible _ partly because as commonplace as these calamities seem, they are relatively rare crimes. Still, a combination of risk factors in troubled kids or adults including drug use and easy access to guns can increase the likelihood of violence, experts say. (AP Photo/Jessica Hill, File)
{}