Climb onto the roof using the dumpster and miscellaneous junk around. Enter the ventilation shaft, and take the southern path. Enter the hallway, and go up the stairs to the lobby. Flip the switch behind the desk, and go through the western doorway to your south into the shooting range. Climb through any of the openings, and open the southeast door. Grab the blue key from the open box in the south of the storage room. Open the next door, and then open the blue bars in the northeast. Take the lift, and go through the cell block to the switch. Flip it, and leave the building through the hole from either the first or second southern cells from the west. Go northeast, and open the northern door. Go around the hall and through the northern doorway. Enter the middle cubicle to the west, and press the switch. Enter the central box at the east, and flip the switch. Return to the outside, and approach the eastern door; you will be lowered into a tunnel. Walk up the rocky stairway, and press on the eastern door.
Other points of interest
On the back side of the desk in the lobby is a switch. Flip it, and the shelf will open to reveal a stairway. (sector 385) Go up the stairs to find a blur artifact, a soul sphere, and the Community Chest logo on the floor.
After opening all the jail cells, go to the southernmost cell in the east to find a panel on the southern wall. Press on it to reveal an opening leading down to a medikit and two backpacks. (sector 387) Open the southern wall to head outside.
In the final tunnel, there is a metal section of wall to the northwest. Press on it to activate a lift upon which a backpack sits. (sector 336) Take it up to return to the upper level.