A 12-year-old student killed a math teacher and critically injured two classmates after opening fire at a middle school in Sparks, Nevada, on Monday morning. The shooter, armed with a semi-automatic gun, died from a self-inflicted gunshot wound. "I heard him saying, 'Why you people making fun of me, why you laughing at me,'" one young witness said. Both injured students are in stable condition, and one underwent emergency surgery. Police have not commented on his motives.