prometheus monitor process Riddles

A dead body is found at the bottom of a multistory building. Seeing the position of the body, it is evident that the person jumped from one of the floors, committing suicide. A homicide detective is called to look after the case. He goes to the first floor and walks into the room facing the direction in which the body was found. He opens the window in that direction and flips a coin towards the floor. Then he goes to the second floor and repeats the process. He keeps on doing this until he reaches the last floor. Then, when he climbs down he tells the team that it is a murder, not suicide. How did he come to know that it was a murder?