Denver high school shooting: Suspect's criminal history and security measures investigated.

Educators at Denver’s East High School were aware that a troubled 17-year-old was on probation from an Aurora weapons criminal charge, so were careful to check him each day for firearms. But the specialized security plan that allowed Austin Lyle to attend classes at East, despite having been expelled from Cherry Creek’s Overland High, unraveled on Wednesday when the administrator who regularly searched him was unavailable. Lyle then ran from the school and drove to Park County, where authorities said he took his own life.