Hint: Defeating Norman Soth:

After you have climbed up the elevator cables and have gotten on top of the other elevator, crawl through the hole in the wall. Norman Soth and two other mercenaries are on the top pathways. While in the hole, there will be one guard on the top path, slightly to the right. You should be able to shoot him in the head. Then, a timer will start and you will have one minute to kill Norman Soth and his other mercenary. When you shoot the first mercenary, drop out of the hole onto the first pathway. The second mercenary will go to exactly where the you shot the first mercenary. Shoot the second mercenary
in the head. Note: The second guard will be aiming at the hole, so he will not see you if you drop out of the hole. The last person to kill is Normon Soth. Start running down the pathway and turn left on the second to last walkway on the left. Look up and turn on your thermal vision. You will see Normon Soth. Get a clear shot and shoot him in the head. After that you must retrieve the smallpox box from the top pathway. If you are on the second to last pathway on the left, go up the ladder. There will be another ladder; use it to climb up. Drop off the ledge onto the pathway. Run down the middle pathway to find the smallpox box.