CENTENNIAL, Colo. - Police on Saturday were looking into the motive of a student who opened fire at a Colorado High School, severely wounding a teenager before apparently killing himself, as the US state sought to understand the latest in a series of shootings.
Karl Pierson, 18, entered Arapahoe High School in a Denver suburb around midday on Friday brandishing a shot gun and asked fellow students about the location of a teacher. He then shot a 15-year-old girl who was nearby, a county official said.
He was later found inside a classroom with an apparently self-inflicted gunshot wound. The teacher, who quickly fled the school, was unharmed.
Fellow students said Pierson was a smart and likeable member of the school's track team and debate club.
Arapahoe County Sheriff Grayson Robinson said detectives were investigating "revenge" as a possible motive, but did not elaborate, though investigators believed the youth acted alone.
Police said they knew of no prior discipline problems.
The shooting in the Denver suburb of Centennial took place just 8 miles (13 km) from the scene of one of the deadliest school massacres in US history, Columbine High School, where two students gunned down 13 classmates and staff before killing themselves in 1999.
There was no indication the incident was related to the anniversary on Saturday of last year's Sandy Hook Elementary School shooting in Newtown, Connecticut, in which a gunman massacred 20 children and six adults before killing himself, Robinson said.
"I believe the shooter knew that deputy sheriffs were immediately about to engage him, and I believe that shooter took his life because he knew that he had been found," the sheriff told a news conference on Friday.
He said a firebomb-like device was detonated inside the school by the suspect, but a second such incendiary device did not go off and was rendered harmless by authorities.