In 2012, Colorado legislators made legal history by passing a law change (Amendment 64) that effectively legalized recreational marijuana use. While supporters around the world celebrated the development, the change in law left thousands of people in Colorado with a pre-legalization conviction. If you or someone you love has a pre-legalization marijuana conviction, you may wonder whether you can do anything about it.  How the American legal system works According to the American legal system, convictions apply according to the law that was in effect when the offender committed the offense.