CENTENNIAL, Colo. — An 18-year-old who wounded a fellow student before killing himself at a suburban Denver school had entered the building 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 Karl Pierson likely was motived by retaliation against a faculty member — probably a librarian at the school — when he opened fire Friday at Arapahoe High School. Robinson said it appears the librarian was the initial target, but that Pierson planned to hurt multiple people.
At a news conference Saturday, the sheriff said the teen bought the pump-action shotgun legally Dec. 6 at a local store. Anyone over 18 is allowed to buy a shotgun in Colorado; only those over 21 can legally buy a handgun.
Also Saturday, Robinson identified the wounded student as Claire Esther Davis, 17. He said Davis was seated with a friend near the door that Pierson used to enter the school when Pierson shot her at close range.
Davis wasn’t a specific, intended target, the sheriff said.
‘‘She is an innocent young lady, and she was an innocent victim of an evil act of violence,’’ Robinson said. Davis remained hospitalized Saturday in critical condition.
Robinson said Pierson bought ammunition Friday and went to the school armed with multiple rounds. The sheriff believes the teen intended to harm many more people but ended up killing himself less than two minutes after entering the school because he knew a sheriff’s deputy was closing in.
Students described Pierson as an outspoken, sometimes goofy, and smart student who often would talk about his beliefs during class, sometimes even debating his teachers. They also said he was an Eagle Scout who finished at the top of speech competitions.
Pierson competed in extemporaneous speaking — in which students prepare short speeches on current events — in the National Forensic League’s national tournament in June in Birmingham, Ala. He didn’t advance to the elimination rounds, the league said.
This year’s school yearbook also listed him as being a member of the cross-country team.
Students said Pierson held communist views and liked to discuss current events and issues, offering his own solutions. None said Pierson was bullied for his beliefs.
‘‘He would speak for himself. He would not be afraid to tell someone how he feels,’’ said Zach Runberg, a fellow senior who had a class with Pierson.
‘‘People would talk to him, nice conversations,’’ Runberg. ‘‘He’s a nice, funny kid. He had some good, intelligent jokes.’’
The investigation into the shooting unfolded as students raised money to pay for medical care for Davis. Friends posted prayers for her on Twitter under the hashtag #prayforClaire.
A fund-raising poster was set up on a fence at the school as students returned to pick up their cars left behind during the shooting.
Chris Davis, a senior, said he helped organize the effort in hopes of helping his classmates and the larger community heal. The poster read ‘‘Warriors always take care of one another,’’ an unofficial school saying.
Davis, whose locker is next to the shooting victim’s, described her as someone who loves horses, has a lot of friends, and always seems happy. He planned to visit her at the hospital Saturday night.
Pierson, whose parents were divorced, lived at least part of the time with his mother in a higher-end neighborhood in suburban Highlands Ranch. The front door of the home was covered with plywood Saturday after authorities conducted a search overnight.
Challon Winer, who lives across the street from Pierson’s home, said he often would see the teen mowing the lawn or shoveling snow. ‘‘I noticed that he didn’t look extremely happy, but he was a teenager,’’ subject to the normal moods of that age group, Winer said.
Winer said Pierson’s mother, Barbara Pierson, has worked with the Neighborhood Watch group and sometimes sent e-mails reminding residents about safety precautions.
He said he didn’t know the family well.
After the shooting, authorities removed students in an orderly procession — a demonstration of aggressive security measures developed by police and schools after the 1999 shooting at Columbine, some 8 miles west.