Once you have rappelled down the wall and into the east wing, sneak up behind the guard and knock him out. Put him on the balcony. Take out the camera, take the data stick, then proceed to the door. Open the door and crouch behind it. You should see one guard patrolling and another standing still. Wait until the patrolling guard is walking away, then sneak into the shadowed part of the hallway. Wait until he is walking away again and open the door to your left. Run up the stairs to the medkit. The guards should not notice you. Proceed down the stairwell by crouching under cameras and shooting lights out. Save your checkpoint at the bottom. Sneak past the first camera and stick to the wall on your left. Take out the other camera near the car and watch from the shadows as the driver inspects the camera, then walks off. Go around the corner to the pillar at the back right and hide on its right side. The guard will return and, after awhile, start smoking. Sneak up behind him, drag him into the dark, and interrogate him. Go back the way you came, in the shadows. Near the door where you entered should be a guard. Stay in the shadows, sneak up behind him, knock him out, and hide his body in the elevator shaft. Sneak past the camera and go back up the stairwell. there should only be one guard in the hall. Knock him out and then hide his body in the darkness near where you acquired the medkit.