CAMBRIDGE — MBTA Transit Police want to know if you recognize the man in the blue Patriots hat and Patriots t-shirt — because they say he beat an elderly rider in broad daylight at Alewife Station last Friday morning, and he is still out there.

The attack happened at 11:25 a.m. on Friday, June 5, in the Alewife busway — the open-air bus loop at the Red Line's northwest terminus in Cambridge. Transit Police's Criminal Investigations Unit released the surveillance photos Monday night, four days into the search, asking riders, commuters and anyone who passed through the corridor that morning to call with what they saw.

Transit Police did not name the victim, list the injuries, or release a physical description of the suspect beyond the surveillance images. The man pictured is described only as a "subject of interest." He has not been charged with any crime as of Monday night.

But the law he is accused of breaking is not a minor one. Assault and battery on a person 60 years of age or older is a felony in Massachusetts, with first offenses punishable by up to five years in state prison.

Alewife is the northwest end of the Red Line, anchoring a multi-deck parking garage and the open-air busway that funnels Red Line riders out to the suburban bus routes serving Arlington, Belmont, and Watertown. Friday at 11:25 a.m. is not the rush hour. It is the quieter midday window between the morning commute and the afternoon school release — the kind of time of day a rider would expect to walk through the busway and not get jumped.

Transit Police did not say whether the elderly rider was waiting for a bus, transferring off the Red Line, or simply passing through the corridor when the attack happened.

The Criminal Investigations Unit is asking anyone who recognizes the man in the photo — or anyone who saw anything at the Alewife busway around 11:25 a.m. on Friday, June 5 — to call MBTA Transit Police CIU with information. Callers can stay anonymous.

The investigation is ongoing.