1. Behind the first M-11 missile is a small uphill path; follow it all the way 
to the end to find the briefcase.

2. After encountering the first heavy armor guard in the mission (a cutscene 
plays showing him walking out of a door), kill him and all the guards, and 
search the platform area. The briefcase is up past a short set of stairs at 
the back of the platform.

3. In the area just outside of Brian Hick's cell, go all the way to the back 
to find the briefcase.