The ACLU of Massachusetts now has a data person on staff, who's begun analyzing lots of data related to criminal justice, and one of his first looks is at "Declining to prosecute" cases for Suffolk County - the sort of thing that new DA Rachael Rollins said she would step up for certain types of low-level crimes:
Her pledge was hailed by progressives and criminal legal reform advocates, but sharply criticized by police lobby groups and others in law enforcement.
In fact, data from DA Dan Conley’s term in office reveal that Rollins’ plan won’t mark a sea change for the Suffolk County DA’s Office. The data show that over half of the charges Rollins has indicated her office will decline to prosecute were dismissed under Conley.
You can download the data, from 2013 and 2014, to take a look yourself.