The security guard was found tied to a chair in the vault, claiming a masked intruder locked him up and stole the diamond. The vault door was locked from the outside with a mechanical deadbolt. However, the guard's wristwatch was missing, and the ticking of the watch could be heard clearly from inside a sealed glass display case across the room. How did the detective know the guard was lying?
The guard staged the robbery.
If an intruder locked the vault from the outside and left, they couldn't have placed the guard's watch inside a sealed glass display case across the room. The guard put it there himself before tying himself up.
About this riddle
Detective riddles are tiny mysteries. Look for the detail in the story that does not fit; it is usually the clue that solves the case.
Difficulty: Medium. More like this: Detective riddles with answers or try Truth & Lie Island for a different kind of puzzle.
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