CENTENNIAL, CO (RNN) - A student who brought a gun to a Colorado high school had a "disagreement" with a teacher and that teacher was "the purpose of the suspect coming to the school," according to Colorado police.
"We know there may have been some controversy, some disagreement between the teacher and the student we know as the shooter and we believe his motive may have been a reaction to that disagreement," said Arapahoe County Sheriff Grayson Robinson.
Police found the suspected Arapahoe High School shooter, identified as Karl Halverson Pierson, 18, dead of an apparent self-inflicted gunshot wound.
A 15-year-old female sustained a "significant" gunshot wound and was taken to Littleton Adventist Hospital. She underwent surgery and is in critical condition.
A second student, initially thought to have received a minor gunshot wound, was not wounded, but was covered in blood of the gunshot victim.
A third student was transported to an area hospital for what police called an anxiety issue.
Robinson said a quick response by law enforcement saved lives. He said that after the school's emergency protocol was implemented, the suspect was discovered five minutes later.
"I have no way of knowing, but I believe the shooter knew that deputy sheriff's were immediately about to engage him and I believe that shooter took his life because he knew he had been found," Robinson said.
Only one weapon, a shotgun, was found inside the school.
"He made no effort to hide it or conceal it as he entered the school," Robinson said.
Police said the shooter was targeting a teacher.
"The student asked for the specific location of the teacher. That teacher was informed of the situation and exited the school quickly," Robinson said. "The was the most important tactical decision that could have been made."
Police found two Molotov cocktails at the scene of the shooting, one which was detonated.
Whitney Riley, a 15-year-old student at the school, said she barricaded herself in a utility room with other students until they heard teachers telling others to run.
Hundreds of students were taken to the track on campus where they were patted down and searched by law enforcement using metal detectors.
Students could be seen waiting to be searched with their hands over their heads. Two pickup sites for parents were established; one at a nearby church, another at a local middle school.
"The response protocols around active shooters were put into place immediately," Robinson said. "The first deputy sheriffs and police officers that were on scene immediately entered the school to engage the shooter if they could locate that individual and also keep these students absolutely safe."
Robinson said the initial call came at 12:33 p.m. MT and the first report of the shooter's death came 14 minutes later.
According to the school's website, 2,141 students attend the school with 118 faculty members. The school has 70 classrooms inhabiting more than 250,000 square feet.
The shooting came almost one year after 20 children and six adults were killed at Sandy Hook Elementary in Newtown, CT on Dec. 14, 2012.
Two seniors at nearby Columbine High School in Littleton, CO, killed 13 people - 12 students and a teacher - on April 20, 1999, before taking their own lives. They injured 24 other students, and police found explosives they had planned to detonate.
Since the Columbine shootings, school security has taken a large turn in the name of keeping students as safe as possible.
According to CNN, administrators have tried to foster school communities that essentially can protect themselves with or without high-tech equipment.
"The first and best line of defense is always a well-trained, highly alert staff and student body," Kenneth Trump, president of National School Safety and Security Services, told CNN.
Physical security at many schools has also been upgraded, and lockdown procedure drills occur more frequently.
In nearby Aurora, CO, in July 2012, James Holmes opened fire in a crowded movie theater during a showing of The Dark Knight Rises, killing 12 and injuring 70.
The former neuroscience graduate student was charged with 166 counts of murder, attempted murder and weapons violations. He pleaded not guilty by reason of insanity.
Holmes' trial had been set for February, but it has been indefinitely postponed so attorneys can argue whether he should undergo another psychiatric evaluation.Copyright 2013 Raycom News Network. All rights reserved.
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