The Adam Smith Institute notes that research shows that deliberate overcrowding and/or inability to defend territory lead to anti-social behavior.
Gee ... what would happen if you uncrowded? Perhaps crime would go down. This is consistent with crime being caused by the random intersection of criminals and victims.
Gee ... what if territory was taken away in something non-judgmental - like an act of god. Perhaps crime would go down.
Readers of voluntaryXchange may have noted that I posted about this phenomenon in post-Katrina New Orleans. Almost two months ago, in "Putting the Lie To Root Causes" I noted that murder disappeared as a crime in New Orleans in the 10 weeks after Katrina.