WOBURN, Mass. — One of three New York City men accused of killing a man in a Harvard dormitory pleaded guilty yesterday to manslaughter in exchange for his cooperation.

Jason Aquino, 21, of Harlem also pleaded guilty to armed robbery and willfully misleading a grand jury.

Blayn Jiggetts had testified that he, Aquino and Jabrai Jordan Copney — a Harlem musician and the son of a retired city cop — went to the Ivy League campus in 2009 to steal marijuana and cash from 21-year-old Justin Cosby. A fourth defendant, Brittany Smith, a Harvard student, pleaded not guilty to hiding the murder weapon.