In such a situation (a crowded bus with people freaking out during the attack), a trained police officer would not attempt to shoot the attacker (unless he was being attacked) because he might easily miss and hit someone else. Or even if he did succeed in hitting his target, the bullet could pass through the attacker and injure or kill someone else. Most people carrying a gun for self-protection would have far less training about such situations, and would very likely be much less accurate since they would not have been working in a job that required regular target range sessions and confronting aggressors in a panic-filled environment.
So it's a good thing that nobody on that bus did have a concealed handgun: The most likely outcome would have been several innocent victims shot, perhaps one or two per bullet in the clip, when the shooter emptied his gun in the attacker's general direction. Or maybe the shooter would have been sitting behind the attacker and accidently killed the driver while the bus was still moving!
On the other hand, maybe bus drivers should be required to carry and be proficient with pepper spray or non-lethal stun guns.
