"The central finding gleaned from the present study was that MML [Medical Marijuana Legalization] is not predictive of higher crime rates and may be related to reductions in rates of homicide and assault. Interestingly, robbery and burglary rates were unaffected by medicinal marijuana legislation, which runs counter to the claim that dispensaries and grow houses lead to an increase in victimization due to the opportunity structures linked to the amount of drugs and cash that are present. Although, this is in line with prior research suggesting that medical marijuana dispensaries may actually reduce crime in the immediate vicinity ."
Robert G. Morris, Michael TenEyck, JC Barnes, and Tomislav V. Kovandzic, "The Effect of Medical Marijuana Laws On Crime: Evidence From State Panel Data, 1990-2006," PLoS ONE 9(3): e92816. March 2014. doi: 10.1371/journal.pone.0092816.