This is a petition to the U.S. government to allow the creation of a federally backed volunteer position and title whereby a civilian could undergo the necessary training to become a first response force through which violent crime up to and including mass murder might be halted with threat or use of lethal force in order to interrupt or halt the crime being committed.
This title will bear with it all the necessary authority from the U.S. federal government to allow said individual to carry a weapon onto any and all premises that he or she deems necessary, civilian or otherwise, as if they had no weapon on their personal at all.
In the same way that air marshals exist to prevent future hi-jackings... these individuals will exist to prevent future mass killings.