Start a game with the setting of Normal . Then on your way to the police station don't pick up anything . When you reach the police station don't go into it . There is a stair case that leads to zombie . The zombie will be hard to kill . If you run out of bullets go into the police station and pick up more . Then go back out to fight him . When you kill the zombie claim the key he drops . Then go into the dark room , and open the locker.