Karl Halverson Pierson is seen in a photo from Littleton Public Schools.
The 18-year-old gunman who wounded a fellow student at a Colorado school before taking his own life Friday was described as a bright, politically opinionated young man who had a beef with the school’s librarian, who had kicked him off the debate team.
Arapahoe County Sheriff Grayson Robinson identified the gunman as Karl Halverson Pierson, 18, a senior at Arapahoe High School in Centennial. Authorities said he entered the school about 12:33 p.m. (2:33 p.m. ET) looking for a specific teacher with whom he'd had an earlier confrontation.
But students who witnessed the attack later clarified that it was the school librarian and debate team coach, identified as Tracy Murphy by NBC affiliate KUSA in Denver, who was the target of Pierson's rage.
Steve Miles is an English teacher who taught Pierson as a freshman, told the Associated Press that Pierson had recently been cut from the debate team, but he didn't know why.
Authorities, who were expected to provide additional information on the attack, which ended with Pierson dead by his own hand and an unidentified female student critically wounded, at a news conference sheduled for 5:15 p.m. ET.
At a briefing on Friday, Robinson said that when the educator learned of the threat, he immediately tried to lure Pierson away from other students by leaving the building.
"It was very tactical for the teacher, for him to remove himself from the school," Robinson said.
Murphy escaped unharmed, KUSA reported, and was escorted by an Arapahoe County deputy on Friday night to pick up a few belongings as police investigated a possible motive.
"'Revenge' is the word that I chose," Robinson told reporters. "This is where our initial investigation is taking us. We know that there was some controversy between the student suspect and the teacher."
Pierson shot a 15-year-old girl before using the same shotgun to kill himself, Robinson said. The girl, who wasn't identified, was in critical condition Friday night, Littleton Adventist Hospital said.
Madison Berry, a senior at the school, said she had taken classes with Pierson.
"He was very outspoken — always involved with class discussion," she said. "So it was kind of odd to see that he was the one who did this."
Abbey Skoda, a junior, told The Denver Post: "He had very strong beliefs about gun laws and stuff. I also heard he was bullied a lot."
Neighbors said Pierson was a nice, quiet teen who lived with a nice, quiet family in a nice, quiet neighborhood.
"They were one of the first (families) to introduce themselves when we moved into the neighborhood" about five years ago, Jo VanDeWege, a neighbor, told NBC station KUSA of Denver.
Pierson "introduced himself and his sister, and they were all very sweet and seemed very cheerful. So this has been quite upsetting," she said.
Diane Shea, a neighbor, agreed, telling the Post, "They're just a normal middle-class family, like many of the families around here."
Pierson's parents divorced in 2011, and he was believed to have lived with his mother, Robinson said late Friday. Authorities were investigating four locations: the school, Pierson's car, his mother's home and his father's home, he said.
Pierson's mother, a school system employee, was out of town caring for a sick relative, neighbors and investigators said.
Watch World News videos on NBCNews.com
First published December 14 2013, 1:16 PM