To quote him,
CheckYourGunStats.com is my current side project. It is a site to view crime rates, murder rates, assault rates, and robbery rates for the USA as a whole as well as each individual state. ....
This is no simple process. But it's coming along. Every data point will be cited. Once again, the purpose of this site is simply to show data in a meaningful manner and to give users an idea of what key events (just legislation based) have happened over the years. It's not to sway anybody one way or another. My opinions are kept off of this site.
Go read the rest of what he has to say about it. I think it might come in handy.