Only kill soldiers that have been taken over by a Body-Snatcher, do not kill any of the regular soldiers. Dispose of any regular soldiers with non-lethal means such as the Wu Silent Pistol. You must not alert anyone. You can tell if a Body-Snatcher is inside a soldier or not when marking them. Normally, a soldier has a blueish color when marked, but a Body-Snatcher gives off a greener color.

Immediately after taking care of the 12 enemies, head over to the main gate at the Admin Building and run away from the building straight to the trailer with the locked red door. Open it and you'll find a launcher inside. During the portion of the mission where Body-Snatcher guards spewed out of the gates of the Admin Building, I used the launcher and fired from afar as they ran out. Remember, you must not be seen. Be careful when you happen to enter reflex mode, if you take too long here sometimes the camp will go into full alert for a quick second even if you barely managed to get rid of the enemy that spotted you.