CENTENNIAL, Colo. – A teenager who opened fire at a suburban Denver school, wounding a fellow student before killing himself, entered the school with a shotgun, a machete and three incendiary devices in his backpack and had ammunition strapped to his body, authorities said Saturday.

Arapahoe County Sheriff Grayson Robinson said Friday’s shooting at Arapahoe High School by 18-year-old Karl Pierson likely was motivated by retaliation against a faculty member, probably a librarian at the school.

Robinson said it appears the librarian was the initial target, but that the gunman planned to hurt multiple people.

Associated Press