Commissioner Raymond Kelly of the New York Police Department came forthwith too little, too late when he issued a memo directing officers not to arrest people caught with small amounts of marijuana unless the drug is in plain public view. A 1977 law decriminalized minor possession, yet tens of thousands are arrested every year.

In 2010, more than 50,000 people were arrested for possession of marijuana; a vast majority of them were racial minorities and male. Civil rights lawyers say that many of them were stopped as part of the Police Department’s broad stop-and-frisk practice and were arrested after officers told them to empty their pockets, which brought the drugs into open view.

Commissioner Kelly’s memo now makes clear that displaying the drug must be an “activity undertaken of the subject’s own volition” and that individuals may not be charged with violating the law if the marijuana “was disclosed to public view at an officer’s direction.”

While the memo, reported by WNYC last week, is an important step, it does not by itself end the problem. The United States Justice Department and New York lawmakers should investigate the legality of practices that led to the arrests of hundreds of thousands of people since the mid-1990s.