Donelli Marinelli was one of Don Tattaglia's capos.
Marinelli ran Tattaglia operations in Brooklyn from their social club, the Ambassador. He had evidence that the Corleone's were paying off a police chief and began blackmailing the chief. However, his greedy scheme got way out of hand and a hit was sanctioned against him by Sal Tessio.
During a break at the Ambassador club, Aldo Trapani gained access and smashed Marinelli's skull in with a baseball bat, before escaping from the confused and shocked patrons of the club.
Donnie Marinelli was murdered by Aldo Trapani, a Corleone enforcer.