"It takes a good guy with a gun to stop a bad guy with a gun."

[Double Naught Spy]

The Hoosier Hero did exceptionally well. Being armed and knowing how to shoot well enough made all the difference in this situation. Mass shooters aren't just stopped by good guys with guns. More often than not when cops aren't involved and shooters are stopped by somebody, it is by citizens without firearms, usually by going hand to hand (wrestling, tackling) or using an improvised weapon (usually as a blunt for object), commonly but not always during malfunctions or reloads by the shooter. I am not downplaying the gun aspect, but pointing out that mindset and a will to act are huge factors in stopping mass shooters. This guy had it all.