Yesterday New York City officially ended all prosecutions for marijuana possession and use, a move that many saw as finally upholding the city's promise to decriminalize cannabis. But it turns out this could've been accomplished 40 years ago.

During the 1970's, New York state underwent a huge increase in marijuana arrests as police officers began targeting college campuses and concert venues for arrest people for using cannabis. The problem became so large that the state legislator had to step in. They passed a bill in 1977 that would make marijuana possession a ticketable offense, not a crime. They thought this would end the mass arrests for marijuana offenses.

And it did! By the early 1990's, arrests for marijuana dropped below 1,000 per year. To put that in perspective, last year there were over 5,000 arrests for marijuana possession in New York City despite it technically being decriminalized.

So what happened? Well in the original 1977 bill, Democrats made a concession to attract Republican voters that said while possessing marijuana was not a crime, if the cannabis was in public view it could still be considered a crime. So after two decades of low arrests, in the late 1990's New York City police officers found a loophole to the law. They could ask people to empty out their pockets, and if marijuana fell out when they did so, they could be arrested and charged with a crime because the marijuana went from being hidden from the public to open to it.

Marijuana arrests went from less than 1,000 per year in the early 1990's to over 50,000 per year in the early 2000's. In 2014, New York City Mayor Bill de Blasio ordered the NYPD to stop using this policy to arrest people for marijuana, and while arrests did drop, they were still above an acceptable limit for de Blasio and other decriminalization proponents. So that's why de Blasio and others in law enforcement enacted the new policy to end arrests for marijuana possession and use.

The hope is that marijuana arrests will drop by 96 percent under the new laws, so there will only be a couple hundred arrests (and presumably even less prosecutions) in the coming years.

Of course, if the police had simply followed the law and not found a loophole in the late 1990's, this wouldn't have been a problem in the first place.

(h/t New York Times)