A wealthy merchant reported his diamond necklace stolen from a velvet display box. The night watchman stated he patrolled the hallway every twenty minutes and saw the necklace sparkling in the moonlight through the glass window the entire night. Detective Ray arrested the watchman immediately. Why?
Diamonds sparkle when refracting light, but they do not emit their own light by moonlight alone unless a direct light source hits them, or more simply: moonlight doesn't hit that north-facing window.
Actually, a simpler logical trap: The watchman claimed he saw it sparkling in the moonlight, but there was a total lunar eclipse that entire night with thick, overcast storm clouds blotting out the moon.
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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