Make you way to the door where the guard tells you he will not let you in because you are not a familiar face. Turn around. Go off the stage. Climb up the steps on your left. Then, go up the stairs on that side. Move up the stairs until reaching the top. On the right side down the hallway is a case on the wall. Inside the case is an ax. Use the ax on a person or body. Executions immediately detach a head, where as hacking at a corpse requires a few swings. Pick up the head. Run back to the door and equip the head as a weapon. Go to the door and press Action. The guard will let you in.