BRIGHTON—A Harvard junior is alleging that a Boston Police Department (BPD) officer beat him up after arresting him about two weeks ago.

Although Garett D. Trombly ’03 has not filed formal charges, his attorney alleges that after Trombly was arrested for drinking alcohol in public, resisting arrest, and assault and battery on a police officer, he was brought back to the police station, where Sgt. Harry A. Byrne Jr. hit him repeatedly in the face, breaking his jaw.

Mariellen Burns, the director of the office of media relations for the BPD, said although no complaint had been filed against the officer who allegedly assaulted Trombly, BPD’s internal affairs division would be conducting a preliminary investigation into the allegations.

The night began at 2021 Commonwealth Avenue between Foster and South Streets, just outside the Boston College campus, on Sept. 9, a little after midnight. That, however, is as much as the two sides of the story have in common.

Byrne, the officer alleged to have assaulted Trombly, declined to comment, deferring to his superior, Cpt. William Evans. Evans’ office referred all calls to BPD’s public relations office, which declined to comment beyond Burns’ statement.

In a Boston Herald article Sept. 11, Evans, who commands the Allston-Brighton District, was quoted denying the allegations, saying, “Nobody was taken away by ambulance and nobody complained that he was beaten up.”

An incident report shows a more detailed police account of the night.

Police say Trombly, along with high school best friend and Boston College (BC) junior Thomas J. Davis, were drinking beer with friends outside of 2021 Commonwealth, Davis’ residence.

When Byrne approached the group and told them to leave, the police report says, Trombly spit and made offensive remarks as he walked away.

Trombly’s attorney, Andrew Good, speaking on his client’s behalf, denied this. Good insisted that his client would only comment through him.

The police report says Byrne then called for back-up and arrested Trombly. The report adds that Trombly “put his hands” on the officer during the arrest.

There is no other mention of violence in the police incident report, which simply says that Trombly was taken back to the station “and booked in the usual manner.”

But Good alleges that the manner in which his client was treated was far from usual.

“During [a]completely unprovoked attack, Trombly…suffered from a close-fisted blow to the head,” Good said.

Once he was released from the station, Trombly had himself admitted to a local hospital. Oral and maxillofacial surgeon Dr. Claude L. Fontaine of Arlington later diagnosed and treated Trombly for a broken jaw.