http://www.care2.com/causes/gun-laws-really-do-stop-gun-violence.html

Since gun laws differ widely between states, CAP looked at gun violence on a state-by-state basis. These comparisons were enough to make a telling conclusion: the 10 states with the strongest gun laws had over three times fewer rates of gun violence than the 10 states with the weakest gun laws.
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To accurately measure violence, CAP looked at data in ten different categories for each state:

1. Overall gun deaths
2. Gun suicides
3. Gun homicides
4. Gun accidents
5. Mass shootings
6. Female homicides committed by romantic partner
7. Gun deaths of minors
8. Gun deaths of police officers
9. Gun deaths by police officers
10. Guns that were sold in a state, then brought to another state to commit a crime

Each state was ranked, 1-50, in each category, and the scores were combined to make one aggregate score.
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The states with a lot of gun violence that could use some common sense restrictions stat include Louisiana, Alaska, Mississippi, Wyoming and Arizona. On the flip side, the states that should be looked to as examples for reducing violence through gun restrictions are Massachusetts, Hawaii, Rhode Island, New York, New Jersey and Connecticut.

By CAP’s own acknowledgment, the research depicts a correlation, not causation. With this data, there’s no way to scientifically prove that the gun laws are the reason for the lack of violence, other than the link between the two things being remarkably strong.