In The Departed (2006), there is a brief firefight between Costello's crew and the plainclothes officers tailing Capt. Queenan after Queenan is thrown from the roof of 344 Wash.
All of the crew has prior offenses as is evident in Capt. Ellerby's presentation which features mugshots of all of them.
"Fitzy. Off-the-boat-psycho, lives with his mother, who's straight out of going my way. Delahunt, muscle. French, the number one."
Why don't the cops regroup and go after these guys later? They're known offenders, their pictures are in the system. Did the plainclothes officers not get a good look at them?