Can an armed citizen intervene the moment a mass shooting happens, and eliminate the shooter?
Most of the mass shootings happening here are school shootings, but mass shootings can happen anywhere. So if a legal gun owner intervenes in the event and eliminates the shooter before they can kill more people, would the gun owner be in trouble for it?
Addendum: Also, if the gun owner has a rifle, can they also use the rifle? I know that civilians can't carry rifles for self-defense, but this is in the case where either the shooting happened nearby, or the owner happened to be driving to the range and wanted to use his rifle.
Addendum 2: If a civilian who does not have any license to own a firearm nor even has one, but does know how to operate and use it effectively, happened to have access to another person's gun with the owner's permission and knowledge, would the two face trouble if it is used to eliminate the shooter?