Gunman made earlier threat against teacher: sheriff

CENTENNIAL, COLO. — Security procedures adopted after the 1999 massacre at Columbine High School helped to put a quick end to a shooting attack Friday, Colorado’s governor said.

The attack occurred at nearby Arapahoe High School by a teenager who may have been nursing a grudge against a teacher and intended to harm him and inflict numerous other casualties.

Karl Pierson, 18, fired six shots from a pump-action shotgun between the moment he walked into Arapahoe on Friday and the moment he killed himself in a library as a school security officer closed in on him, said Arapahoe County Sheriff Grayson Robinson.

Arapahoe senior Claire Davis, 17, who was sitting with a friend when Pierson entered the library, was shot in the head. She remained hospitalized in critical condition Sunday. Hundreds of students held a candlelight vigil for Davis on Saturday night at a park near the school.

Pierson’s attack lasted just 80 seconds but reopened scars in a community traumatized by mass shootings in nearby Denver suburbs — at Columbine High School in 1999 and at an Aurora movie complex in 2012.

It came one day before the first anniversary of the Dec. 14, 2012, massacre at Sandy Hook Elementary School in Newtown, Conn., in which 20 children and six educators were killed.

Robinson has said investigators think Davis was shot at random by Pierson, who had gone into the school looking for a teacher with whom he had a dispute.

Fellow students described Davis as a vibrant senior and equestrian with a lot of friends. Pierson may have been nursing a grudge against the teacher — a librarian and head of the school debate team — since September. Pierson managed to ignite one Molotov cocktail inside the school library before he killed himself as a fast-acting school security officer, a deputy sheriff, closed in, Robinson said.