The thief is planning to steal something from your house in the middle of the night. He snuck inside your house and stole a few stuffs. Before he leaves, everything was locked - the doors, the windows, even the trapdoors. He tries to find a way to get out of the house but he can't find any. Since it was hard to see things in the dark, he saw a figure which was you. He was frightened by your sighting since you're the owner of the house.