Do you recognize this man?
Police said he attacked another passenger on the southbound platform at Andrew Square station just before 6 p.m. last Sunday.
The assailant was described as a white man between 35 and 40 years of age, with dark hair, a green hooded jacket and blue jeans.
Anyone with information about the incident or the person in the above photograph should contact detectives at 617-222-1050.
Those wishing to remain anonymous can also text a tip to 873873 or using the anonymous feature on the department's SeeSay app.