Four suspects, one true statement

Question

Exactly one of four suspects, A, B, C or D, committed a crime. Each makes one statement, and exactly one of the four statements is true.

A: "B did it."
B: "D did it."
C: "I did not do it."
D: "B is lying."

Who committed the crime?

Accepted Answer

C did it. Test each culprit. - If A did it: A's statement is false, B's is false, C's ("I did not do it") is true, D's ("B is lying") is true. Two true. Not allowed. - If B did it: A's is true, B's is false, C's is true, D's is true. Three true. Not allowed. - If C did it: A's is false, B's is false, C's ("I did not do it") is false, D's ("B is lying") is true. Exactly one true. Allowed. - If D did it: A's is false, B's ("D did it") is true, C's is true, D's ("B is lying") is false. Two true. Not allowed. Only C works. A shortcut. B's statement and D's statement contradict each other, so exac…

Four suspects, one true statement

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