Transit Police report arresting two South Boston residents and a Dorchester man on charges they beat a man on a Red Line train and two women who tried to come to his aid on Sunday.
Police add they obtained an arrest warrant for another South Boston man for his alleged role in the attacks on a train entering Broadway station.
Michael Davis, 36, of South Boston, Patrick Joyce, 24, of Dorchester and Kristine Mullen, 20, of South Boston, are scheduled for arraignment on a variety of assault-related charges on Tuesday in South Boston District Court.
They surrendered themselves at Transit Police headquarters, police say. Kevin McCarthy, 21, of South Boston, is still sought, police say.
Police initially said six people were involved in the beatings; they did not specify the status of the two other people captured on video.