Besides, this isn't the movies. You don't go charging in hell bent unless you are begging to be blown away or want a lot more civilians dead or taken hostage. Look at that school in Russia. You don't want to be arrested by Russian police as they have much more leeway to beat or kill you. But still they couldn't stop the shooters before the damage was done. This type of thing with someone willing to take their own life, as with Terrorists, is almost impossible to combat.