On the last stage (Los Angeles Airport) after you get through the parking garage you come to a room with a guard in a booth to your left and a female janitor right in front of you. In this room you have two options to advance. #1) The first option is to go through the guards booth by either luring him out and then running in before the door closes, or use the door code(its either 1387 or 1687). #2) The second and eaiser option is to go into the bathroom opposite the guard booth and climb through the vent in the wall this will take you to the same place as the other way and you won't have to deal with the guard.