Move around the pillar and look to the right for a broken railing that you can jump over. You will see the prisoners body on the floor. There is usually one on the bridge if you are quick knock him out and turn around to see another that you can quickly knock out. Return to the area where the officer was torturing the prisoner and be careful for any guards. There is also a decent silenced weapon down here for later in the game if you want to take it. Put on your gas mask and enter through the gate, getting you a moral point and also a safe.

If it is showing green switch it off and head down stairs. Head through the door on the right and look to the left for a breaker. Move into this area and look for a safe key near a pillar on the right side. Switch this off and then quickly knock that guard out. As you move forward you can interact with a generator. Listen to the conversation for a moral point. As you get to the top of these stairs you will hear guards talking. You can't do anything about this, so turn left and make your way up the metal stairs. You will hear an officer and guard torturing someone. Make your way over this and turn the light off on the pillar. Turn around as soon as the conversation ends and move forward until you see a bridge on your left. Head down and hide next to some sandbags and listen to the two guards having a conversation, at the end of which you'll receive a moral point. Look to the left to see a stairway leading down. Now turn around and return back to the beginning of the level. If you are quick you can open the box on the table below the red box to get night vision goggles. Wait for the heavily armoured guard to walk away, then crouch and sneak towards where the guards originally were. Hide to the left in an alcove for the light armoured guard to approach and knock him out. You will see two guards, one is heavily armed. Now turn around and make your way to the end of the tunnel, switching off any light on the way.

Hide behind it and listen to the entire speech for a moral point. When the level starts, turn the light off to your left and sneak up to the railcar in front of you.

Metro 2033 key generator