Hanlin held a grudge against Jack Bauer after Bauer arrested his partner, Seth Campbell, for taking bribes. Hanlin never forgave Jack for this.
Hanlin was assigned as Bauer's backup during an operation to capture a suspect. Both Bauer and Nina Myers were deeply disturbed to learn this, but the assignment had been made by Division and it was already too late. Hanlin later taunted Jack by telling him of how Campbell's wife killed herself. As he repeatedly harassed Jack, Myers called George Mason to try keep him in line. Later, as the suspect, Alan Morgan, made an escape, Bauer ordered Hanlin not to engage, but Hanlin ignored orders. He shot in the leg, making him fall to his death over a banister. ("Day 1: 5:00pm-6:00pm")