Take the spiral stairs down to the lower level
From Create Your Own Story
You gingerly head down the spiral stairs, remembering what happened at the end of the last set...
At the bottom, you find a long hallway that appears to dead end in a concrete wall at one end, and has a security door that appears to open into the weapon and drug area you saw from above. You are on the end with the security door and the stairs. It's a good thing you snuck down the stairs as there is guard with a machine gun hanging at his side with his back to you, reading a newspaper under a dim light at the start of the hallway. He sits at a rickety desk facing the expanse of the hallway, which is also dimly lit. You could probably take him out. You could also try heading into the drug and weapon area, but it is brightly lit and you don't stand much chance of going unnoticed.