Run up to the northwest area of the first screen to get the sniper rifle in the building. He'll see you, so run. Then you need to find him. Use the Directional Microphone and wave it all around you; if you can't hear his breathing then he's probably on another screen. Once you have a direction, use the Thermal Goggles and the map screen to see if you can spot his position. If you can, use the sniper rifle and blast away. He'll run. Use the Thermal Goggles to see his footprints, repeat until he finally dies. Oh, and don't stand around like a retard looking in first-person view mode forever, because he will come up behind you and one-hit kill you. And don't ever save. HAVE FUN