WaPo has the article: See Emily Badger's No, legalizing medical marijuana doesn’t lead to crime, according to actual crime stats which cites a study from the Program in Criminology, University of Texas at Dallas, titled The Effect of Medical Marijuana Laws on Crime: Evidence from State Panel Data, 1990-2006.
Those jurisdictions that implemented medical marijuana legalization, according to the researchers, experienced "no noticeable local uptick among a whole suite of crimes: homicide, rape, robbery, assault, burglary, larceny, and auto theft." (Quote from Emily Badger.)
But there was also a decline in assaults and murders. Why? Maybe this: "Given the relationship between alcohol and violent crime , it may turn out that substituting marijuana for alcohol leads to minor reductions in violent crimes that can be detected at the state level."
Now there's an unanticipated consequence.