Karl Pierson: Portrait of the Arapahoe High School shooting

A bright student who voiced strong opinions in class and on the debate team (especially about gun rights), dividing his time between divorced parents, some suggestions that he might have been bullied now and then, a run-in with a teacher who had ordered him suspended when the student threatened the man.

On the surface, and like so many other school shootings, there seems to have been an accumulation of events – warning signs, perhaps – why Karl Halverson Pierson might have taken a shotgun to Arapahoe High School in Centennial, Colo., looking for the teacher with whom he had had a disagreement but shooting a girl who happened to be in the wrong place at the wrong time before ending his own life in an empty classroom just minutes after walking into the school.

Informed speculation, but speculation nevertheless. And it’s likely to be some time before the full story behind this “unspeakable horror in a place of learning,” as Colorado Governor John Hickenlooper put it Friday, is told.

Here’s what officials and others – mainly fellow students – are saying about 18 year-old Mr. Pierson and about what unfolded.

Pierson had been a member of the school’s debate team, but had been kicked off the team by the debate coach, identified in several news reports as Tracy Murphy, who is also the school’s librarian. At some point, Pierson was suspended from school for having threatened Mr. Murphy.

When Pierson entered the school at about 12:30 pm Friday, carrying a shotgun he made no effort to conceal, he immediately began shouting for Murphy.

When the teacher heard that he was being targeted, he left "in an effort to try to encourage the shooter to also leave the school," Arapahoe County Sheriff Grayson Robinson said. "That was a very wise tactical decision."

Pierson fired several shots, hitting – although apparently not targeting – a 15 year-old female student, who is now being treated at a local hospital and listed in critical condition.

Two suspected Molotov cocktails were also found inside the school, the sheriff said. One detonated, though no one was injured.

Some students have suggested that Pierson was picked on at times, although he wasn’t afraid to push back verbally.

“I had class with him and knew he was very outspoken and willing to contribute, and also that he had a controlled temper he would use during discussion,” Carl Schmidt, a fellow senior, told the Los Angeles Times.

"A lot of people picked on him, but it didn't seem to bother him,” Thomas Conrad, who had an economics class with Pierson, told the Denver Post.

High school senior Frank Woronoff told CNN he had known Pierson since they were freshmen together.

"He was the last person I would expect to shoot up a high school. He was honestly incredibly humble and down to earth. He was a little geeky but in a charming way," he said.

As gunshots echoed through school hallways, teachers immediately began following the school’s protocol – locking doors, turning off lights, and herding students to the back corners of classrooms or into storage rooms. It was a tactic schools adopted after the 1999 Columbine High School massacre in nearby Littleton, Colo. When everyone scrambled to escape, some jumping from windows and racing through the firing zone.

Senior Megan Jeffords, 18, was singing Christmas carols in the hall with her choir class when the shots rang out. A teacher rushed the 18 singers into a closet, where they huddled for more than half an hour, the Associated Press reported.

Hours later, after Ms. Jeffords was reunited with her father, she was still visibly shaken and unable to talk much about what happened.

The school resource officer – an Arapahoe County deputy sheriff – immediately went looking for the source of the gunfire. By the time he found it, Pierson had shot and killed himself.

Other police officers and sheriff’s deputies had followed the same post-Columbine protocol – immediately entering the school in search of the shooter rather than setting up a perimeter around the school and waiting for SWAT teams to arrive.

Sheriff Robinson says this likely saved lives.

"This kid, the officers went right to him literally within minutes," Gov. Hickenlooper said at a press briefing Friday. "That is a world of change from the way response used to happen."

Students are shocked that another school shooting has now involved them, perhaps more so that the shooter was a classmate who had wanted to go to the US Air Force Academy in Colorado Springs.

Looking for reasons behind the attack – as well as such details as where Karl Pierson got the shotgun – authorities have obtained search warrants for Pierson’s mother’s home in Highlands Ranch, his father’s home in Denver, and his car, found in the school parking lot.