Transit Police arrested a registered sex offender for performing a lewd act on an MBTA Green Line train on Thursday night.
According to police, officers responded to the Coolidge Corner station, where a female witness told officers the man was conducting himself in a lewd manner.
She moved away to another seat in the trolley and contacted police.
The suspect, later identified as Robert Widberg, 53, of Canton, Massachusetts, was arrested and charged with open and gross lewdness.
During the investigation officers learned Widberg was a registered level 2 sex offender.
It's not if Widberg has an attorney.