New information from documents that were received by the Associated Press now say the teenager who shot another student to death in Arapahoe High School Dec 13, initially put out death threats, but wasn't considered a high threat and was allowed to return to class.

Reports show Karl Pierson, the 18-year-old who gunned down a fellow student, said he would target and kill the coach of the debate team - following an incident where Pierson was downgraded from captain of the debate team.

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Pierson reportedly entered the Denver-located school with a shotgun and a machete looking for the coach, but his plans quickly turned awry as he killed an innocent 17-year-old girl and later killed himself when school security officers were surrounding him.

Pierson had a history of anger and temper tantrums with the school including being sent home after hitting classroom doors just two days before the incident.

Considering that mass shootings now occur more often, many people feel the threats should have been taken seriously.

Lori Horn, mother of recent graduates from Arapahoe High, believes school authorities should have been worrying less about his privacy and more about the security of the rest of the students. 

"When the threat happened, why was there tolerance for it? If there's a threat, if there's a concern, you need to address it," she said.

Schools typically focus on preparing security measures if a gunman situation were to occur, and less on trying to prevent these situations from occurring beforehand.

However, being able to determine whether a threat is real or not is much easier said than done.

"There's always the question of how do you really know," said Kenneth Trump, of the National School Safety. "When you're dealing with human behavior, it's not a simple check-the-box, yes-or-no, black-or-white answer. It's gray." 

TagsArapahoe High School, Karl Pierson, school shooting, death threat