Fact check on I-594 FBI claim

I-594 supporters can tell you that Women are 38% less likely to be shot to death by their partners in states with compulsory background checks.  They claim the US Department of Justice, Federal Bureau of Investigation, Supplementary Homicide Report of 2010 proves this claim.

How can they say that?  Plow through those FBI reports for yourself (links 1, 2, 3, 4, 5, 6,).  Nowhere is the data broken down by state, or the presence of that state's laws requiring background checks.

Do you think maybe the I-594 freaks are making stuff up?