Debunking the “good guy with a gun” myth
It’s difficult to say if a mass shooting has ever been stopped by an armed civilian. For every source that lists an occasion when a civilian was able to stop an active shooter, there are three sources ready to point out that the “civilian” involved was really off duty or retired military or that the shooter was out of rounds anyway. Frankly, it’s difficult to evaluate the intentions of a shooter, so it appears that that