Press the button in this room and move on to find more enemies. Once they are defeated you should head through the area on the left to head into a room that contains an Elite Guard (3/3) and an ammo crate:
Press the button in this room and move on to find more enemies. Once they are defeated you should head through the area on the left to head into a room that contains an Elite Guard (3/3) and an ammo crate: