I dont really want to get into the debate about gun laws but the causal link has been something of a holy grail for economists. Look at earlier posts and reactions to get an ides of the complexity of trying to pin down causation.
So I'll leave this study for all you econ geeks to discuss, here is the graph reported on in the O:
Though you can't argue causality you can make the case that there is a pretty strong correlation and explanations that suggest that the true causal link is opposite (as some would argue) are a pretty big stretch. It is hard to see how restricting firearms makes us less safe...
However states with little firearm affection are both more likely to pass legislation and less likely to have firearm deaths. So is it the legislation that is driving the low deaths or other unobservable state characteristics?