Take a look at them state by state, and compare to their firearms laws.
Washington DC before the Heller case had some of, if not the most restrictive gun laws in the US, yet had a homicide rate that was something like 4 or 5 times the national average.
I'll go look for some stats and post them here if I find them.
Edit:
http://www.infoplease.com/us/statist...ate-state.html
This shows a murder rate of 21.9/100,000 for DC vs 11.2 for the next highest state.
This compared to Montana with 2.6 where anyone of legal age can open carry, and concealed carry anywhere except in town, and they can conceal there too, but need a permit.
Alaska has 4.4 and I don't believe there is any state restrictions at all.
If you were to go through every state, and compare the murder rates to the gun laws, you'd probably find very little correlation, as opposed to if you started to study demographics and social conditions.
For example Jamaica has a complete firearms ban, and one of the highest murder rates in the world. In 2005 they had 58 murders/100,000 people.
The only thing gun control does, is keep victims defenseless.