Dead body Found at the bottom of a multistory building

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 off from one of the floor for attempting suicide.

A homicide detective is called to look after the case. He goes to the first floor and walks in 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.

The he goes to the second floor and repeats the process. He keeps on doing it till 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?

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At each floor, the Detective did the same task of opening the window and flipping the coin. If it was a suicide, then at least the window at any of the floor must have been left open by the person who jumped off. The present situation only suggests that someone pushed him off and then closed the window again.