Prohibition and Homicide Rates
"The data are quite consistent with the view that Prohibition at the state level inhibited alcohol consumption, and an attempt to explain correlated residuals by including omitted variables revealed that enforcement of Prohibitionist legislation had a significant inhibiting effect as well. Moreover, both hypotheses about the effects of alcohol and Prohibition are supported by the analysis. Despite the fact that alcohol consumption is a positive correlate of homicide (as expected), Prohibition and its enforcement increased the homicide rate."
Jensen, Gary F., "Prohibition, Alcohol, and Murder: Untangling Countervailing Mechanisms," Homicide Studies, Vol. 4, No. 1, Sage Publications: Thousand Oaks, CA, February 2000.