The teenager who opened fire at a suburban Denver high school on Friday, hurting a fellow student before turning the gun on himself, was identified as 18-year-old Karl Halverson Pierson who may have been seeking revenge on his former debate coach for dropping him from the team.
Carrying a shotgun, Pierson stormed Arapahoe High School in Centennial at around 12:30 p.m. local time, calling out the name of Tracy Murphy, who coaches the school's debate team, according to NBC. He shot and critically wounded a 15-year-old female student before killing himself.
The wounded student underwent surgery and was in critical condition, according to The Associated Press, which reported that two suspected Molotov cocktails were also found inside the school, one of which detonated but without hurting anyone.
Police initially said two students were shot, but later clarified only one had been wounded. More than 2,100 students attend the school.
Pierson was removed from the debate team and suspended from school in September for a few weeks after threatening Murphy, New York Post quoted Joe Redmond, 18, one of three co-captains on the team, as saying. He had earlier won contests on his speech and debate team.
After the body of the shooter was found inside the school – within 20 minutes from the first shot heard – all students were taken to Shepherd of the Hills Church, from where family members picked them up.
Pierson was described by neighbors as a "nice young man," according to KUSA. He was also described as an achiever, an athlete, who had also worked on an Eagle Scout project.
Arapahoe County Sheriff Grayson Robinson narrated the incident, which took place on the eve of the anniversary of the school shooting in Newtown, Conn.
"The gunman came into the school and immediately asked for the location of a very specific teacher, and he named that teacher by name," CBS quoted Robinson as saying.
"When the teacher heard that this individual was asking for him the teacher exited the school immediately, which was in my opinion the most important tactical decision that could have been made," he said. "He knew he was the target and he left that school in an effort to try to encourage the shooter to also leave the school with the focus of safety and security and wellbeing of our students in his mind."
The shooter took his life because he knew that he had been found, Robinson added.
After they heard the firing, some students hid in their classrooms. "They were safer inside their locked schoolroom classes than they would have been had we allowed them to exit, and that was part of our strategy and part of our protocol," the sheriff told reporters.
A school janitor told KMGH he saw a student dressed in tactical gear running through the school. "It just looked weird," the janitor was quoted as saying. "He went in and I heard two pops. That's when I knew. I said, 'They are shooting in the school.'"
After calling 911, the janitor escorted the targeted teacher out of the school.
The shooting took place about 10 miles from Littleton, where shooters Eric Harris and Dylan Klebold killed 12 students and a teacher at Columbine High School in April 1999 before killing themselves.