Why does someone become a mass shooter? Researchers are interviewing perpetrators and their victims—and those who narrowly averted committing a mass shooting—and discovering a common thread of psychological despair. Can their work be applied to the prevention of future violence? Guest: Jillian Peterson, forensic psychologist, violence researcher, and author of The Violence Project.  If you enjoy this show, please consider signing up for Slate Plus. Slate Plus members get benefits like zero ads on any Slate podcast, bonus episodes of shows like Slow Burn and Amicus—and you’ll be supporting the work we do here on What Next. Sign up now at slate.com/whatnextplus to help support our work. Learn more about your ad choices. Visit megaphone.fm/adchoices