https://www.sciencedaily.com/releases/2018/07/180724110031.htm

Clearance rates -- the number of cases solved, typically by the arrest of a suspect -- were falling for violent and property crimes in the two states before they authorized retail sales of marijuana late in 2012. The rates then improved significantly in Colorado and Washington while remaining essentially unchanged in the rest of the nation, according to the researchers' analysis of monthly FBI data from 2010 through 2015.

"Our results show that legalization did not have a negative impact on clearance rates in Washington or Colorado," said David Makin assistant professor in WSU's Department of Criminal Justice and Criminology "In fact, for specific crimes it showed a demonstrated, significant improvement on those clearance rates, specifically within the realm of property crime."