"suicide" from a window

A woman died from falling out of a window of a 100-story building and landing on her back, breaking her neck. While they knew it was from a window, they weren’t sure which. They also were unsure if this was suicide or murder.

A detective was called and he performed a small experiment.

He went to the second story, opened the window, took out a coin and tossed it out the window, it landed on heads.

He performed this with every window in every story, opening their windows and tossing a coin out, each time landing on heads.

After he performed this with all the windows, he confirmed that this was a murder and not a suicide.

How did he figure this out?