When Adam Lanza stormed into the Sandy Hook Elementary School in Newtown, Conn., on Dec. 14, 2012, opening fire on schoolchildren and sending kindergartners scrambling into closets for protection, American news outlets immediately began asking the desperate question, “Why?” What made Lanza into a school shooter and mass murderer? Was it his family background, his reported autism, his political viewpoints, even his time spent in homeschooling? Thoroughly profiling the perpetrator has become the first response of the American media in every shocking crime from Sandy Hook to the Boston Marathon bombing and more. But almost one year to the date...