LITTLETON, Colo. (CBS4) - Warning signs were ignored or weren't detected.
A door was left unlocked.
Those are some of the factors that are cited in reports released this week about the December 2013 shooting at Arapahoe High School and factors experts are now making a close review of.
Claire Davis was killed by a fellow student in the shooting and the shooter killed himself afterwards.
The reports were commissioned by Davis's family along with the Littleton Public School District.
On Thursday night the authors of the reports met with the board of the school district, and many at the meeting said they hope school officials across the state are paying attention to the issues that are being raised.
The most glaring issue the experts found about the shooting was the repeated soft handling of the shooter, particularly after he made a death threat to a teacher.
"There were a lot of behaviors going on that never got reported to the people who could do something, never got reported to the disruptors," Dr. John Nicoletti told the school board.
Littleton Schools Superintendent Brian Ewart said in the meeting that there has been an increased emphasis on mental health issues in the district in the two years since the shooting.
"This board has committed to mental health $810,000 (for) full time equivalencies -- social workers, psycologists and counselors -- in all of our schools that weren't there before, and it is making a significant impact," Ewart said.
The district has said it has also changed its documented threat assessments.
"I think that we still have some more work to do in evaluating the best way that we approach threat assesments, danger assessments," Ewart said.
The experts said a majority of schools and districts in the state don't have threat assessments at all.
Another suggestion came from Professor Linda Kanan of the University of Denver who would like to see the anonymous student tipline Safe2Tell expanded and standardized across Colorado.
"This might be a good time for the state to say we support a statewide effort to make sure that information gets out not just through the schools but to all of our communities," Kanan said.
The experts who studied the case say many of the issues raised are not unique to Arapahoe High School. They recommend that parents should question their own districts to make sure their safety procedures are getting the same scrutiny as they are in Littleton.
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