San Francisco District Attorney George Gascón announced today that his office will proactively expunge and seal the records of misdemeanor marijuana offenders, the San Francisco Chronicle reports. The office will also resentence offenders who received a felony pot conviction.

Proposition 64, the 2016 referendum item that legalized recreational marijuana in California, allows pot offenders to petition for resentencing if their crime would have received a different penalty, or no penalty at all, under the new law.

Rather than wait for petitions, Gascón's office is searching for eligible cases.

"The district attorney said his office will dismiss and seal more than 3,000 misdemeanor marijuana convictions in San Francisco dating back to 1975," reports the Chronicle's Evan Sernoffsky. His office will also likely resentence "thousands of felony marijuana cases."

A member of the California Assembly has introduced a bill that would make all Prop. 64–related expungements and resentencings automatic.

Retroactivity is a powerful tool for righting drug war wrongs, but prosecutors are often opposed to the practice. In Colorado, another state that has legalized marijuana, Assistant Attorney General Kevin McReynolds has reportedly declared that there's "nothing irrational about holding someone accountable for a crime under the law in effect at the time." If voters had wanted legalization to apply retroactively, he said during a 2016 hearing on retroactivity, "all they had to do was say so."

At the federal level, the United States Sentencing Commission voted in 2014 to let tens of thousands of federal prisoners apply for retroactive sentence reductions after the commission changed the guidelines for drug trafficking.

But Congress failed to extend retroactivity to federal crack cocaine prisoners convicted before the Fair Sentencing Act passed in 2010. The new law substantially increased the amount of crack required to trigger a mandatory minimum sentence, and the failure to make it retroactive has left thousands of prisoners serving sentences that Congress has deemed excessive.