Start out with two teams with one person on each team. On the "Planning Screen" 
tell the other person to go wait at the 3rd. floor door.Start the Mission. 
Take your person and go down the ladder and watch where the guard goes by putting 
your map on full screen. As soon as he passes the corner, go into the room across 
the hall and turn the alarm off. Then shut the door. Switch to the other person. 
Take that person and go through the door and to the right. Go into the room with 
the computer an download the files. This took me several times.