Riddle: The residents of Belle View, a 5 story posh building, witnessed a dead body lying on the premises.
Mr. Park, the famous homicide detective was called. He climbs the building and on every floor he opens a window and flips a coin out the window.
On doing the same thing on the fifth floor, he knows it was a murder, not a suicide.
What do you think?
Answer: He must have been trying to see how something that was thrown from the window would land, as opposed to simply dropping it (which is what a Suicide would look like)!
After the killer kills him. He would have escaped after closing the window. So the detective had unable to open window in 5th floor.