gun rights advocates often push to arm more people, citing prominent examples where a “good guy with a gun” stopped a “bad guy.”

“It’s direct, indisputable, empirical evidence that this kind of common claim that ‘the only thing that stops a bad guy with the gun is a good guy with the gun’ is wrong,” said Adam Lankford, a professor at the University of Alabama, who has studied mass shootings for more than a decade. “It’s demonstrably false, because often they are stopping themselves.”

There are approximately 300M guns (including roughly 6 million AR-15 style rifles) in the possession of 120M gun owners in the US. Yet the gun murder rate has declined from 7.3/100k in the 70's to roughly 3/100k in 2014.