CENTENNIAL -- Karl Pierson's attack at Arapahoe High School lasted just 80 seconds -- enough time to shatter Claire Davis' life and leave hundreds of other classmates in fear for their own.
And his intent was far more grave.
He rushed into the school Friday with a bandolier of ammunition strapped to his chest. He carried a machete, three Molotov cocktails and the pump-action shotgun that authorities said he bought days before to avenge a grudge he had against his debate coach.
"His intent was evil, and his intent was to injure multiple people," Arapahoe County Sheriff Grayson Robinson said Saturday afternoon.
She remained in critical condition Saturday night after suffering what the sheriff described as a point-blank shotgun blast to the head.
"She needs your continued prayers," her family said through Robinson.
Davis was sitting next to a friend in the school library about 12:30 p.m. when Pierson, 18, entered through a door on the north side of the building demanding to know the whereabouts of librarian and debate coach Tracy Murphy.
One minute and 20 seconds of surveillance footage captured Pierson's movements through the school, Robinson said.
The teenager fired his shotgun randomly down a hallway. His next shot hit the face of Davis, who collapsed onto the girl next to her, drenching her in blood.
"There was no time for the victim to run from the shooter," Robinson said.
Pierson fired a total of five times and ignited a Molotov cocktail that set ablaze three bookshelves in the library before turning the gun on himself. Police found his body in a corner of the room. By then, Murphy and a janitor had left the building.
"The shooter knew the deputy was coming," Robinson said.
Pierson bought the shotgun legally Dec. 6 and purchased a large amount of ammunition at local stores Friday morning, Robinson said. Colorado law allows an 18-year-old to buy a shotgun but not a handgun.
Investigators searched the school and the home of Pierson's mother in Douglas County, and they impounded his car, which he had parked along a curb in the northside lot, Robinson said. He declined to say what evidence was discovered but said all indications were that Pierson acted alone.
"We found nothing in those search warrants that there were any co-conspirators," Robinson said.
Pierson's mother was out of town Friday when the shootings happened.
The teen apparently harbored a grudge against Murphy after being disciplined by him in September, action that Robinson said was appropriate. The discipline came after Pierson made a verbal threat against Murphy to a group of students. Law enforcement was made aware of that threat, and the response to it remains under investigation, Robinson said.
Still, Pierson had not been suspended from school or kicked off the debate team, where classmates recalled him as a skilled and opinionated orator.
Davis' family thanked first responders and the staff at Littleton Adventist Hospital for saving her life and asked for privacy.
"She's very innocent, humble and sweet, no matter what," said Afton Phelps, a senior and a friend of Davis'. They once went in the same group to a homecoming dance.
Phelps said Davis is a talented equestrian whose bedroom decor revealed her love of horses. The two had been closer in their sophomore year but occasionally grabbed lunch together.
"It's hard to wrap our minds around," Phelps said of the shooting. She and two of Davis' other friends sought counseling Saturday and found many of their classmates doing the same. "It was really helpful to talk about it."
Among them were Chris Davis, who is not related to the victim, and two other seniors, who taped a cardboard sign to the fence, urging their classmates to raise money for the wounded student.
"I don't know her very well. We're just trying to help her family in any way we can," Chris Davis said, adding that the school's morning announcements end with this reminder: "Warriors take care of one another."
"Right now," he said, "we are taking care of a fellow Warrior and her family."
Other students Saturday remained shaken and struggled to find words.
"Waking up today was kind of rough," said Emily Morris, a senior who came to retrieve her car. "You realize it's not a nightmare like everyone wanted it to be."
Morris' concerns were for Claire Davis, with whom she would grab lunch and share schoolwork.
"She is the nicest girl I've ever met. She doesn't deserve this at all," Morris said. "I don't know why anyone would do this to her. It's all so confusing."
Perhaps more confusing is what lies ahead, she said.
"I don't know what it's going to be like to go back inside the school."