After you Laser-Mic the conversation between Masse and Grinko in the glass elevator, kill the three guards in the courtyard and climb the skirting into the South Wing. You will reach the room with the elevator. Hide on the left side of it, aiming your pistol at head level towards the elevator. Two guards will run out. Kill them, but do not waste your time hiding their bodies. Get into the elevator that they came from and go to the seventh floor. There will be a glass door with a keypad on either side of the hall. Go to the one on the right and move back and forth in front of the door. The soldier in there will see you and run to the door. Back up so you will not block the door. Let him unlock the door, and as he is opening it, get your sights on his head. It will not move after the door is opened. The second the door is open all the way -- fire. Do the same on the other glass door. This is a good strategy to get clean head shots.