(Newser) – It turns out that when you make it easier to buy guns, more people wind up getting killed with guns. That's the conclusion researchers from John Hopkins University came to after studying the effects of Missouri's 2007 repeal of its "permit-to-purchase" law, which required a local sheriff to vet would-be gun owners before they could buy their weapon. Researchers believe this move was "associated with an additional 55 to 63 murders per year" over the next five years, they announced.

That jump "did not happen with homicides that did not involve guns; it did not occur to any neighboring state; the national trend was doing the opposite—it was trending downward," the study's lead author tells the BBC. Researchers say they also controlled for factors such as unemployment, poverty rates, burglaries, incarceration, policing, and other state laws. More criminals got their hands on guns as well; the number of handguns being recovered from crime scenes shortly after crimes doubled. But Barbara Shelly at the Kansas City Star expects the study to fall on deaf ears in Missouri's legislature. "They favor a vigorous gun market, and no amount of research or evidence is going to convince them otherwise." Indeed, the state senate last week endorsed a bill that would nullify all federal gun laws. (Read more Missouri stories.)

