Gunman, 18, wounds classmate at Arapahoe High School

Chris Davis, a senior who plays basketball at Arapahoe High School, hangs a sign to raise money for the victim in a shooting at the school in Centennial, Colo., on Saturday, Dec. 14, 2013. Investigators were working to find out what motivated a teenage gunman to enter his suburban Denver high school armed with a shotgun looking for a specific teacher a day earlier.  The 18-year-old shooter critically wounded a 15-year-old student and was later found dead in the school, apparently of a self-inflicted gunshot wound. (AP Photo/David Zalubowski)
Chris Davis, a senior who plays basketball at Arapahoe High School, hangs a sign to raise money for the victim in a shooting at the school in Centennial, Colo., on Saturday, Dec. 14, 2013. Investigators were working to find out what motivated a teenage gunman to enter his suburban Denver high school armed with a shotgun looking for a specific teacher a day earlier. The 18-year-old shooter critically wounded a 15-year-old student and was later found dead in the school, apparently of a self-inflicted gunshot wound. (AP Photo/David Zalubowski)