The teenage gunman who killed a teacher and a 15-year-old pupil at his old St. Louis high school left a note calling his lonely life a “perfect storm for a mass shooter” — and was armed with enough ammo to kill hundreds. Orlando Harris, 19, left a manifesto-like note in his car before storming Central Visual and Performing Arts High School with an AR-15-style rifle and at least 600 rounds of ammo Monday, killing two and injuring seven others, police said Tuesday. “He wrote, ‘I don’t have any friends. I don’t have any family. I’ve never had a girlfriend. I’ve...