Detective Thorne interrogated four suspects regarding a stolen diamond. Alice said Bob did it. Bob said Charlie did it. Charlie said Bob is lying. Diana said she didn't do it. Only one person is telling the truth. Who stole the diamond?
Bob
If Bob is the truth-teller, then Charlie's claim that Bob is lying is false, and Alice's claim that Bob did it is false (she accuses Bob, but Bob is innocent? Wait. If Bob is guilty, Alice telling the truth means Bob did it. Let's re-verify: If Alice is true, Bob did it. Then Bob's claim that Charlie did it is false. Charlie saying 'Bob is lying' would be true (since Bob lied about Charlie). That means both Alice and Charlie are telling the truth, violating the 'only one truth' rule. Let's check Bob as the sole truth-teller: If Bob is true, Charlie did it. Alice lied (she blamed Bob). Charlie lied (said Bob lied—wait, if Bob told the truth, Charlie saying Bob is lying is a lie, which matches!). Diana lied (she did it). Thus, only Bob is telling the truth, making Charlie the thief.
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: Hard. More like this: Detective riddles with answers or try Truth & Lie Island for a different kind of puzzle.
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