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Using data for the period 1980 to 2009 and controlling for state and year fixed effects, the results of the present study suggest that states with restrictions on the carrying of concealed weapons had higher gun-related murder rates than other states.

It was also found that assault weapons bans did not significantly affect murder rates at the state level. These results suggest that restrictive concealed weapons laws may cause an increase in gun-related murders at the state level. The results of this study are consistent with some prior research in this area, most notably Lott and Mustard (1997).
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read more: http://www.tandfonline.com/doi/abs/10.1080/13504851.2013.854294?journalCode=rael20#.Uszge42Q9Ic

The author of this study notes that his findings are consistent with those of John Lott and David Mustard, two researchers who authored a study which found that right-to-carry concealed gun provisions both “deters violent crimes and it appears to produce no increase in accidental deaths.”
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https://peopleagainstillegalguns.org/crime-deterrence-and-right-to-carry-concealed-handguns