there are protocols for going through the school which will take a long time because think about how big a high school is. at columbine high school, one of the things the officers told me afterward which was riveting to hear, naturally people hear gunshots they panic and hide. officers would think they had cleared a hallway, they would go down the hallway and suddenly behind them, out of lockers, out of closets, out of ceilings, students started emerging who had hidden. that was terrifying for officers because they trying to spot a gunman and suddenly saying they're in a very fluid environment. they practiced these protocols a great deal. >> one of the other things i saw a denver post reporter who was on the ground at the time snapping photographs of teachers writing down the names of students who were outside, taking attendance, making sure that they knew who was outside the school. one of the other interesting lessons, i'm not sure if it's post-columbine or more recent