CENTENNIAL, Colo. -- A teenager who may have had a grudge against a teacher opened fire Friday with a shotgun at a suburban Denver high school, wounding a fellow student before killing himself.
Quick-thinking students alerted the targeted teacher, who quickly left the building. The scene unfolded on the eve of the Newtown massacre anniversary, a somber reminder of the ever-present potential for violence in the nation's schools.
The wounded student, a 15-year-old girl, underwent surgery and was in critical condition. Authorities originally said a second student was wounded, but Arapahoe County Sheriff Grayson Robinson said Friday night the other girl taken to a hospital was covered in blood from the other student and wasn't injured.
Sheriff Robinson identified the shooter as Karl Halverson Pierson, 18. The sheriff did not elaborate on any possible motive except to say Pierson had had a "confrontation or disagreement" with the teacher.
Pierson made no attempt to hide his weapon after entering the school from a parking lot and asking for the teacher by name, the sheriff said. When the teacher learned that he was being targeted, he left "in an effort to try to encourage the shooter to also leave the school," the sheriff said. "That was a very wise tactical decision."
Two suspected Molotov cocktails were found in the school, the sheriff said. One detonated, though no one was injured.
The school was swiftly locked down. Within 20 minutes of the first report of a gunman, officers found Pierson's body inside the school, Sheriff Robinson said.
Arapahoe High stands just 8 miles east of Columbine High School in Littleton, where two teenage shooters killed 12 classmates and a teacher before killing themselves in 1999. The practice of sending law enforcement directly into an active shooting, as was done Friday, was a tactic that developed in response to the Columbine shooting.
Colorado has endured other mass shootings, including the killing of 12 people in a movie theater in nearby Aurora in 2012. But it was not until after the Newtown massacre that state lawmakers moved to enact stricter gun-control laws.