Case 309
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.
Sam
“Lane and Peyton are both innocent.”
Harper
“Peyton is guilty.”
Lane
“Rowan is innocent.”
Peyton
“Lane and Rowan are both innocent.”
Rowan
“Lane is innocent.”
Who is guilty?
Solution: Harper
If Harper is guilty, Harper's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.