What bothers me is how few people try to fight back rather than be the victim of a criminal, or in this case, a madman. The first rule of self defense is attack your attacker. This simple maneuver usually throws an opponent off balance. Now granted, in this case it'll be impossible to ever determine what was running through the killers head or whether he would have been fazed by resistance, but going out trying to do something is always preferable to lying down and accepting your fate. Speaking from experience as a security officer, one man can effectively throw a group of aggressive individuals for a loop by coming in and dominating the situation (Read: wading in to the middle and screaming a lot). Most criminals run according to a script where they go in, threaten and face no resistance. When things don't go according to plan they freeze up and start posturing. In the face of continued resistance thsy usually back down and tell you how lucky you are as they walk away. (Then they run when you take after them.)

My point? One person taking a chance and attacking the gunman could have possibly overpowered him, especially if he was counting on his guns to cause people to panic.

I personally think that martial arts training in school could help.