A homicide detective is called at a crime scene. A man is lying dead in front of an abandoned building. It is believed that the man jumped out of the window off the abandoned building and committed suicide. The detective asks his team to collect evidence and he heads toward the building. He goes to the first floor and towards the room that is on the front side. Inside the room he lights a cigarette, walks toward the window facing the dead body, opens the window, and throws out the cigarette. he then goes to the second floor and repeats the same process. He keeps doing the same thing until he is done with all the floors, and then takes the lift to the ground floor. Upon reaching there, he informs the team that it was not a suicide but a murder. How did he know this was not a suicide?