Perhaps you all can help me out...
I've looked a good bit but found no specific info on numbers of registered firearms owners (ie they bought them from an ffl and there is a paper trail showing they legally own them).  Further, I cannot find that info on a state-by-state basis.  
I haven't found any info on crimes committed with firearms that were illegally possessed either.  Any suggestions?
I'm trying to prove a point for class that people who own firearms legally are significantly less likely to use them to commit a crime.  
I know you guys wanna help prove this point...

most states don't have specific registration for a firearm.   The dealer has a copy of your 4473 but the paper trail ends there unless you are in a community that requires you to register.  
 Maybe statistics for concealed carry permits would be easier to find.  Legal owners of machine guns have a spectacular record since 1934 where only one legal machine gun was used in a crime and that was a police officer as I understand it.  There are approximately 350 thousand legal machine guns owned by civilians...I remember seeing the figure somewhere and am still looking since I forgot to keep the figures.  
 The illegally possessed firearms committing crimes is going to be tough.  Many of those people buy the gun legally.   Everytime a repeat felon commits a gun crime it is illegal since they shouldn't be having one in the first place.
 Try the CCW's search.  Post your results for everybody when you finish your research.
good luck.