The gunman who opened fire in Dayton, Ohio early Sunday killed nine people and wounded 14 in just 32 seconds before police responded and took him down.

Dayton, along with the shooting at an El Paso, Texas Walmart the day before, are the most recent mass shootings that show how, despite the presence of trained officers and armed civilians—the people the National Rifle Association would call “good guys with guns”—gunmen can inflict horrific casualty counts within seconds, before anyone can respond. Experts on violent crime say such incidents make clear that despite the NRA’s post-Sandy Hook justification, relaxing gun laws to let more people to arm themselves has done nothing to prevent mass shootings.

It’s likely to make things worse if armed civilians intervene when shootings erupt in public places, says John Donohue, a Stanford Law School professor whose research has focused on gun violence and policy. “Unless you’re very well trained, you usually add more to the body count than you subtract,” Donohue says.

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“The weaponry he had was so dangerous,” says Donohue. “Allowing citizens to continually be able to ratchet up the fire power available to them is really unwise policy.”

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“It really is unbelievably lucky how effective the police response was in these recent mass shootings,” Donohue says. “And there were probably loads of people carrying weapons around and they did nothing. You can’t expect them to.”