I find it very hard to believe that population density has no connection to violence. I know for a fact that studies on rats (the link is to a very brief abstract only) indicate exactly the opposite: the denser the population, the more pathology there is among rats. This chart and map suggest that density and violence are very closely correlated. By the way, I think it's unfair to treat DC as if it were a whole state since the lower densities in the non-urban areas even in a place like NJ dilute the violence. DC is all urban all the time.
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