When Oliver Queenan was meeting with the undercover man in Costello's crew, Fitz led a group to attempt to take out the undercover. While the undercover got away, Fitz and the gang killed Queenan by tossing his body off the roof of a building. As they made to leave, Fitz yelled at Costigan for being late before cops watching Queenan opened fire on them. In the shootout, Timothy Delahunt was mortally wounded. Fitz wounded a cop as they got into the van and made their escape.
He screwed up a body dump when he failed to dump Delahunt's body in the marsh to where it would not be discovered. He carried a Smith & Wessen Model 36 revolver. He was killed when a drug shipment pickup was busted by Boston police, taking a bullet between the eyes.
He was portrayed by David O'Hara, a Scottish actor. The similar, while distinct, accents of the Irish and Scottish enabled O'Hara to naturally portray an Irish-born gangster.