Bangchan was an assassin. He broke into your and your parents house in the late night and killed your parents. After the murder he was cleaning up the evidence. He didn't know that you were in this house.

Suddenly, you opened the door of your room, standing in the door frame, in rather old clothes. You were untidy, bruised and thin. Even when you were only 4 years old

Bangchan didn't see or hear you, so he just kept cleaning the evidence