A heavily armed teenage shooter who fired a fatal shotgun blast at a fellow student at a Colorado school before killing himself was a "murderer" who intended to claim many more victims, Arapahoe County Sheriff Grayson Robinson said Monday.
The lone victim, 17-year-old Claire Davis, was shot point-blank in the face while she sat in the hallway of Arapahoe County High School in the Dec. 13 attack.
The high school senior, who was apparently a random victim, died eight days later.
Robinson, providing reporters in Centennial, Colo., with additional details on the shooting, said the entire incident lasted only about 80 seconds, The Denver Post reports.
The shooter, 18-year-old Karl Pierson, also a student at the school, shot Davis in the hallway where she was sitting then went to a nearby library where he killed himself as a unarmed security guard -- a retired deputy sheriff -- closed in.
"No question the person who entered the school is a murderer," Robinson said. "He intended to hurt [a] maximum amount of people."
The sheriff said Pierson, who was armed with a 12-guage shotgun, carried more than 125 rounds of ammunition strapped to his chest and waist on a pair of bandoliers and also a machete and Molotov cocktails.
He said the shooter apparently intended to track down a librarian who had disciplined him and to whom he had made verbal threats months ago.
Robinson told reporters that Pierson had written on his arm the names of several classrooms that apparently were intended as targets. He had also written a Latin phrase that, translated to English, reads: "The die has been cast."
The shooter was still in the planning process as recently as 30 minutes before the shooting and had bought some additional ammunition.
"He took time to have a meal ... went bowling alone," Robinson said. "No question it was a very deliberate and planned event."
Robinson said the door that Pierson entered is supposed to be locked but rarely is because it is inconvenient.
The sheriff acknowledged that the shooting would forever change the community.
"It's up to us to decide whether it changes us for better or worse," Robinson said. "We will be better for this. There is no question."
Contributing: Associated Press