Training is well and good but you never know what a person will do in certain situations. The only people I trust are Marines and those that have been in combat situations. They have performed and most police officers will get in the way of a bullet to save,I know that for a fact,but not all!
When death is cracking past your head your decisions have to be fast and correct. If the armed deputy was safe under cover, but NOT under fire, then you would think he would move to a more strategic position to do his job. He was armed, the students being shot were not.