Study: Missouri murders spike after state repeals gun background check law
This is fairly damning of the "background checks don't matter" argument.
Also, as far as I can tell this doesn't measure the impact on suicides, which it's difficult to imagine would be zero.
http://www.rawstory.com/rs/2014/02/17/study-missouri-murders-spike-after-state-repeals-gun-background-check-law/
In the study which will be published in an issue of the Journal of Urban Health, a team of researchers led by Johns Hopkins Center for Gun Policy and Research Director Daniel Webster found that between 55 to 63 more people were murdered each year after Missouri repealed its permit-to-purchase (PTP) handgun law in 2007.
This study provides compelling confirmation that weaknesses in firearm laws lead to deaths from gun violence, Webster said in a press release. There is strong evidence to support the idea that the repeal of Missouris handgun purchaser licensing law contributed to dozens of additional murders in Missouri each year since the law was changed.
...
While murders in Missouri spiked between 2007 and 2012, bordering states experienced no significant increases. And the overall murder rate in the U.S. declined by 5 percent during that same period.
Coincident exactly with the policy change, there was an immediate upward trajectory to the homicide rates in Missouri, Webster told BBC. That upward trajectory did not happen with homicides that did not involve guns; it did not occur to any neighbouring state; the national trend was doing the opposite it was trending downward; and it was not specific to one or two localities it was, for the most part, state-wide.