Narcosis

In Chapter 5, “Back To Normal”, you will invert the level. You will have to thrust over some desks a few times and go through doors. When you finally reach a flat, non-desk surface, instead of carrying on search for another door in the same vein as you have been. Follow this tunnel all the way and you will see a body behind some bars. He has ID tags, so you can pick them up here if you didn’t get them earlier.