Funded by a US Department of Justice grant, the WSU team looked at 12 years of crime clearance rates from Colorado and Washington and compared them to the US average, as well as to other states singularly.
The study reported: “Our results suggest that, just as marijuana legalization proponents argued, the legalization of marijuana influenced police outcomes” in a positive way. Incident clearance rates “grew more in Colorado than in the rest of the country for all crime types except aggravated assault and motor vehicle theft, and similarly rose more in Washington than in the rest of the country for violent crimes and burglary.”
Legalization is correlated to better clearance rates, but it may not be causing them.
“While our results cannot specifically explain why police clearance rates have increased in Colorado and Washington,” the team reported, “we think the argument that legalization did in fact produce a measurable impact on clearance rates