"The homicide rate increased from 6 per 100,000 population in the pre-Prohibition period to nearly 10 per 100,000 in 1933. That rising trend was reversed by the repeal of Prohibition in 1933, and the rate continued to decline throughout the 1930s and early 1940s.[48]"
http://www.cato.org/pubs/pas/pa-157.html