Start by clearing everyone out of the level. Then meet with the man that gives you the .50 caliber sniper rifle. Next, go to the gate that the motorcade drives through, Wait directly beside the gate until the motorcade comes through. Once you have your sight on the man you have to kill, shoot him then run off to the left of the level. Hide behind one of the buildings. Ditch the sniper rifle and do not leave any guns in your hands. Find a U.N. guard that you can sneak up on. Sneak up behind him and strangle him with the Fiber Wire. Note: You will not fail the mission when you use the Fiber Wire. Pick up the M4 and run to the exit.