A tour group was walking through an old museum when everyone in the group heard a loud, high-pitched scream and a slam. They all went down to the room in which the scream came from. The only thing in the room was a door. The door was closed and there was a suicide note pinned onto it. One of the men walked to the door and opened it to see was was inside. It was a drop-off. There was no place to stand; It was just a big pit. An investigator named Shadow immediately declared it was murder, not suicide.
How did he know?