German investigators: Munich gunman had researched mass killings, planned attack for at least a year - AOL

German investigators: Munich gunman had researched mass killings, planned attack for at least a year - AOL: "Sonboly, who was not previously known to police, apparently suffered from depression and was receiving psychiatric treatment. A 14-year-old who went to Sonboly's high school told The New York Times' Rukmini Callimachi that Sonboly had been severely bullied at school. "She claims that he had an altercation several months ago with a classmate at school and threatened to 'go on a shooting rampage,'" Callimachi reported. Still, Sonboly's motive remains "fully unclear," Andrae said. He had evidently researched previous killing sprees, prosecutors said. A book entitled "Rampage in Head: Why Students Kill," was found during searches of the home he shared with his parents in Dachauer Strasse, in the Munich suburb of Maxvorstadt."