Seth Carver is what is euphemistically termed "a piece of work", but then Narcotics Detective is no job for angels. The team bump into him, literally in Esposito's case, when trying to track Jerry Tyson and Ryan's old service pistol as "Kick the Ballistics" kicks into gear. To maintain his cover in the bar where Beckett attempts to talk to him, he rabbits, then flashes his badge when they're alone. Seth is carrying a Glock 17, which is what Ryan had, but he's also hiding a dirty secret -one that causes Ryan to assault him.