Report: Arapahoe High Shooter Showed Warning Signs That Were Missed

January 18, 2016
Photo: Arapahoe High School shooting anniversary 2
Arapahoe High students and supporters holding a candle light vigil and watch as 14 white balloons symbolizing the Colo. students killed in school shootings since the 1999 Columbine school massacre are released, during a remembrance ceremony marking one year since the shooting at Arapahoe High School, in Centennial, Colo., Saturday, Dec. 13, 2014. 

Littleton school district officials admit warning signs were missed leading up to the deadly Arapahoe High School shooting in 2013, according to school district reports released Monday. ​A threat assessment by the district was conducted on the shooter, Karl Pierson, just months before the attack. Yet he was deemed a low risk, and allowed to return to school. Now, the superintendent of Littleton Public Schools admits the threat assessment was incomplete. More: Arapahoe High School Shooting Reports Show Missed Signs About Gunman.