When the aforementioned arrest of Flack's colleague, Truby, results in the release of a serial killer, Flack berates Mac, who angrily counters that they both want the man back behind bars. They put aside their indignation to collar the murderer once more. Flack is mere feet away when the man plummets from a roof, handcuffed, and lands on a police cruiser, fatally wounded. Looking up, he sees Mac staring down at him from where the suspect fell (episode 3.21, "Past Imperfect").