Timothy Delahunt was a member of Frank Costello's gang, who was possibly an undercover Boston police officer.



Delahunt was later shot by police after assisting in the murder of Oliver Queenan, and . He was bleeding on a couch at the gang's hideout when Fitz came over and told him that a doctor was coming but traffic was slowing him down. He called over Costigan and revealed that he knew Billy was the rat because he knew to go to 344 Wash even though Delahunt mistakenly told him to 314 Wash. Delahunt dies before he could alert the other gang members. The SIU plants a story on the local news that Delahunt was a cop, attempting to assure Costello that his rat was gone in order to take the heat off of Costigan. 


Delahunt dies from blood loss after being shot