CENTENNIAL, Colo. (AP) — A sheriff in Colorado says the high school student who critically wounded a classmate before killing himself on Friday may have planned to attack five rooms inside the school.

The sheriff in Arapahoe County says 18-year-old Karl Pierson had written on his arm letters and numbers corresponding to the Arapahoe High School library and four nearby classrooms.

Investigators are trying to determine whether Pierson had planned to attack people in those rooms.