CENTENNIAL - Investigators released updated information about a shotgun attack Arapahoe High School that fatally wounded a 17-year-old girl.
Arapahoe County Sheriff Grayson Robinson started the news conference Monday morning on the Dec. 13 shooting at Arapahoe County High School with a moment of silence to honor the victim.
Claire Davis, a senior at the school, was shot point-blank in the face. She died Dec. 21 after spending eight days hospitalized.
Authorities say another Arapahoe High student, 18-year-old Karl Pierson, shot Davis and then took his own life as a deputy sheriff closed in.
"No question the person who entered the school is a murderer," Robinson said. "I absolutely know the murderer had evil intent. [He was] bent on causing the largest amount of harm to the largest number of people."
Robinson said the door Pierson entered through is supposed to be locked but rarely is because it's inconvenient.
Robinson says Davis appeared to be a random victim and that Pierson probably intended to track down a librarian who had disciplined him.
"Claire Davis was murdered," Robinson said. "We had learned things about Claire I wish I had never learned. She was preparing for [her] life of purpose."
Robinson went on to say the entire shooting took only 90 seconds.
The sheriff says the shooter also had a machete and Molotov cocktails and likely wanted to hurt many others.
Robinson mentioned Monday morning that up until 30 minutes before the shooting, the shooter was still in the planning process. He bought 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 admitted the shooting will 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."
The memorial for Claire Davis is set for Wednesday at 1 p.m.
It will happen at The National Western Events Center, where Claire was scheduled to compete in equestrian events next month.
(KUSA-TV © 2013 Multimedia Holdings Corporation with The Associated Press)