he host of the show (Piers Morgan) actually said that no civilian/ armed citizen has ever stopped a mass shooting and that it is a "myth" that it has been done.
Perhaps you could supply some links.
I only recall one incident, where a school employee went out to his car to retrieve a weapon. Can't remember whether that person actually stopped the shooting.
In other cases the shooting was stopped by unarmed students or adults and by private security as in the attempted church shooting.