TODAY | December 14, 2013
>> mott is on the scene for us this morning. ron, good morning.
>> reporter: good morning. we should get more details about the shooting later today when officials meet with the media later on. there are a lot of questions in the meantime, about why this young man would do this's police believe he was out for revenge as you've eluded. an eerie scene at an american school . students filing out with hands on their head after gunfire erupts inside.
>> we heard police coming in and police talking on their radios and screaming and shouting and i didn't hear any of the shots but it was scare why.
>> reporter: police say 18-year-old karl pierson , a student at arapaho high school , walked in armed with a shotgun and looking for a teacher. police say it stemmed from an early confrontation or disagreement between the two.
>> when the teacher heard this student was asking for him the teacher exited the school and for me was the most important tactical decision that could have been made.
>> reporter: the chaotic frant tick scene was similar to sandy hook and ten miles away , columbine high school in 1999 . officials credit a school janitor who started pierson and tripped an alarm in the ble auilding and exiting the teacher to safety. still one student was shot while three others suffered what the sheriff called anxiety attacks. officials say pierson was pound dead from what appeared to be a self-inflicted gunshot wound as officers closed in.
>> the officers got to him and got to him literally within minutes. that is a world of change from the way response used to happen.
>> reporter: police were late into the night searching for evidence, including at pierson 's home.
>> it's just heart-wrenching to find out somebody is out there that wants to hurt people.
>> the student shot who attends arapaho high school at last report is listed at critical condition and classes have been canceled on monday.