On the roof, Costigan catches Sullivan off-guard and handcuffs him. As Costigan had secretly arranged, Trooper Brown (Anthony Anderson) appears on the roof as well. Shocked, Brown draws his gun on Costigan, who attempts to justify his actions by exposing Sullivan as Costello's mole. Costigan asks Brown why Dignam did not accompany him as Costigan had requested, but Brown does not answer. Costigan leads Sullivan, his hostage, to the elevator. When it reaches the ground floor, Trooper Barrigan (James Badge Dale) shoots Costigan in the head, then shoots Brown, and afterward reveals to Sullivan that Costello had more than one mole in the police. Sullivan then shoots and kills Barrigan. At state police headquarters, Sullivan identifies Barrigan as the mole and recommends Costigan for the Medal of Merit.