The cops in the school, holding the hallway, were in a no-win situation: if they defied orders to contain and charged in and kids got killed, they'd be crucified for not holding and waiting for a "real" entry team to make entry. If they held, as they did, kids got killed. If they threw in flash bangs and the shooter went berserk, they'd be criticized for not being patient and re-escalating what they might have seen as a hostage situation. (I can hear my old command..."What the hell was wrong with you? You just initiated action without orders and kids died. How many kids died from friendly fire?") The protocol of going to the shots worked except the shooter survived the initial confrontation and was able to hole up (thanks, Captain Obvious) but at least he wasn't free to roam the entire school, al la Columbine and others.
One of the commanders was explaining the delay, saying that "If unprepared officers charged in, thee bad guy could shoot them, and then grab up the dead cop's weapons. He would also grab up a police radio and then he could listen in to our plans."
You can always make up an excuse for inaction.
