Assault

On the first floor, door slam and punch out patrols near the door. If this attracts attention, stand at the doorway and punch everyone out until they stop coming.

Grab a shotgun. Fire a single shot to attract most cops on the floor. Stand back and shoot them in the doorway.

If you run low on ammo or run out and enemies remain, throw your weapon and engage in close-quarters punching. Pick up a weapon and resume shooting until they stop.

If the Stage Clear screen does not appear, there are still enemies in the far south room. Equip a gun and eliminate them.

Pick up the 'S' puzzle piece located inside the south-west bathroom on the first floor.

Grab a gun and proceed to the elevator.

On the second floor, shoot the first enemy and aim east. Shoot the cops and detectives as they approach. Walk out to equip a dead enemy's gun as needed.

Stay in the elevator and continue shooting until enemies stop coming. Eliminate any remaining scattered enemies one by one.

Exit through the elevator.

On the third floor, punch out the enemies to the immediate north and south.

Equip a shotgun. Aim west into the hallway and west room, and kill as many enemies as possible with one or two shots.

Back up and eliminate any enemies who enter the hallway to find you.

Equip a shotgun and aim north. Strafe left and shoot toward the chief's office. You can eliminate all enemies in this area with a couple of these strafe runs.

Use this strategy to also eliminate any wandering patrols in the central hallway.

Eliminate the final cops, a group in the north-west and a single cop to the north, using a shotgun.

Pick up the keys from the north-west office.

Open the cell in the north-east. Talk to the guy inside, then eliminate him.

Search the north-east room on the top floor of the police station in Chapter 13 to find the Richter mask.

Return to the north room and pick up the file.

Leave to the car to complete the mission.