- "I'm gonna kick your fuckin' ass."
- ―Mulkey to John McClane.
Mulkey was posing as a construction worker at the airport's annex skywalk at the new terminal, alongside O'Reilly, Sheldon and Shockley, to oversee that the antenna array is blown up. Then Dulles chief engineer Leslie Barnes and five airport SWAT officers arrived, as they predicted. After O'Reilly sprang the bottleneck ambush by killing the SWAT team's commander, Mulkey killed two SWAT officers while Sheldon killed the other two officers, though Shockley was killed by a SWAT officer.
Suddenly, John McClane unexpectedly arrives from an air duct and kills O'Reilly. Both Sheldon and Mulkey underestimated McClane's resourcefulness despite their efforts to kill him. After McClane pushes the working rig down and crushing Sheldon to death, Mulkey sees that the scaffolding attached to the working rig pins McClane down near the annex skywalk. When Mulkey tried to kill McClane, he finds the ammo in his last magazine.
As Mulkey was getting closer to him to engage him in a close quarters fight, McClane used a pipe to press the button that activated the skywalk. Because McClane is pinned to the ground with debris, he has to wait for his Beretta 92FS pistol to come to him. Mulkey saw this and rushed to beat McClane to it, but McClane got hold of it first, and emptied multiple rounds into Mulkey's chest with it, killed him. He was the fourth mercenary killed by McClane, and the fifth of Stuart's group to die during the operation.