Case 289
The Vanished Key
A locked evidence cabinet was opened without permission.
Rule: exactly one suspect is guilty. The guilty suspect lies. Every innocent suspect tells the truth.
Kai
“Emery is guilty.”
Emery
“Either Kai or Riley is guilty.”
Parker
“Kai and Riley are both innocent.”
Riley
“Kai is innocent.”
Quinn
“Riley is innocent.”
Who is guilty?
Solution: Emery
If Emery is guilty, Emery's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.