A simple hypothesis: in states where cannabis is legal, police can spend more time and resources investigating more serious crimes. While this seems obvious in theory, a recent study provided concrete evidence that it does happen in states that legalize cannabis.
A Police Quarterly study, released in July, found that serious crime clearance rates were increasing in states that had legalized cannabis consumption. According to Marijuana.com, this clearance rate increase has been most prominent in Colorado.
According to an excerpt of the peer-reviewed study, "findings suggest no negative effects of legalization on crime clearance rates."
While overall cannabis-related arrests have decreased significantly in Colorado and Washington, clearance rates for rape, robbery, aggravated assault, burglary, larceny and motor vehicle theft have increased.
Marijuana.com quoted the study lead David A. Makin, an assistant professor of Washington State University’s Department of Criminal Justice and Criminology:
> There is an opportunity cost to every activity an officer engages in. Marijuana arrests can take hours of time. When it’s legal, you no longer have to expend those hours. The data seem to suggest that this is what has occurred.