Drug Decriminalization and Violent Crime
"Generalizing from the findings on Prohibition, we can hypothesize that decriminalization would increase the use of the previously criminalized drug, but would decrease violence associated with attempts to control illicit markets and as resolutions to disputes between buyers and sellers. Moreover, because the perception of violence associated with the drug market can lead people who are not directly involved to be prepared for violent self-defense, there could be additional reductions in peripheral settings when disputes arise (see Blumstein & Cork, 1997; Sheley & Wright, 1996)."
Jensen, Gary F., "Prohibition, Alcohol, and Murder: Untangling Countervailing Mechanisms," Homicide Studies, Vol. 4, No. 1 (Sage Publications: Thousand Oaks, CA, February 2000), pp. 33-4.