Mitchell (Day 4)

Mitchell was the main desk security guard at Felsted Security in Burbank during Day 4. He was a habitual smoker.

Day 4
Mitchell checked Jack Bauer and Audrey Raines into the Felsted building so they could work with Gary to identify a terrorist suspect on film footage. The suspect, Henry Powell, sent a team of hit men to protect himself, and Mitchell was among the first people killed by them.

When Jack noticed that the guard was not at his desk, Gary simply assumed that Mitchell had gone out for another smoke. But bodies on the live feed proved otherwise.