ST. LOUIS: A 19-year-old who killed a teacher and a 15-year-old girl at a St. Louis high school was armed with an AR-15-style rifle and what appeared to be more than 600 rounds of ammunition, a police official said Tuesday.

Orlando Harris also left behind a handwritten note offering his explanation for the shooting Monday at Central Visual and Performing Arts High School, St. Louis Police Commissioner Michael Sack told reporters. Tenth-grader Alexzandria Bell and 61-year-old physical education teacher Jean Kuczka died and seven students were wounded before police killed Harris in an exchange of gunfire.