The parents of Colorado school gunman Karl Pierson said Monday that they are "shattered" by the shooting and don't understand why he critically wounded a classmate and then killed himself.
"We are shattered by the tragic events that took place on Friday at Arapahoe High School," Barbara and Mark Pierson said in a statement issued by a family spokeswoman.
The couple said they were praying for the 17-year-old senior Pierson shot in the head as he hunted for the school staffer who had benched him on the debate team.
"Our thoughts and prayers are with Claire Davis and her family. They, and she, have suffered unimaginably, and we pray for her full recovery. We also pray for the entire Arapahoe High School community, as we know your lives are forever changed by this horrific event.
"As parents, we loved our son Karl dearly and we are devastated by what happened Friday. We cannot begin to understand why Karl did what he did. We ask for privacy during this unthinkably difficult time and hope that you will respect our need for time to grieve."
A classmate told NBC News that Karl Pierson was an avid reader of a notorious bomb-making bible, "The Anarchist Cookbook" and was packing a grudge against debate coach Tracy Murphy, the school librarian.
“Speech and debate was his life, and the fact that he wasn’t there crushed him a little bit and made him really tense and angry,” Joe Redmond, the team co-captain said.
He said Pierson and Murphy “did not get along, and whatever it was escalated to a death threat.”
At midday on Friday, Pierson showed up at the Centennial, Colo., school with a pump-action shotgun, ammunition strapped to his chest, a machete and Molotov cocktails — and headed for the library.
Alerted to the threat, Murphy left the building, which police praised as a tactical move to lure Pierson outside.
Pierson fired one round down a hallway and then shot Claire Esther Davis, 17, who just happened to be sitting nearby with a friend. He killed himself as a security officer closed in on him, police said.
Murphy was not hurt in the attack. A statement from the Littleton Public Schools said that he had “asked that we share his and his family’s concern for all of the victims of this tragedy.”
Claire was in critical condition, stable but in a coma, her family said in a statement released through the hospital.
Police said she and Pierson were not friends.
Redmond said he spoke to Pierson as recently as Monday about the possibility of returning to the debate team.
“I did try to help him and didn’t get to him,” Redmond added. “No one was able to get to him. At the end of the day, that’s what happened.”
He added: “The Karl that I knew was a good person, but obviously the Karl who came into the school on Friday was not.”
NBC News' Ron Mott contributed to this report.