Correlation between marijuana and crime?

A study conducted by PLOS One which looked at the crime rate across the country between 1990 and 2006 (a period where 11 states legalized medical marijuana), crime fell throughout the United States. So according to this study, there is NO evidence suggesting that the legalization of marijuana will lead to an increase in crime. This is a slap in the face to those opponents who believe that the legalization of marijuana in states will lead to the "gateway" of other, more serious drugs such as cocaine. The new study may be a great factor in causing opponents to change their mind or become more open to the idea of legalizing marijuana. What do you think?

Source: The Washington Post