Case 138
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.
Marley
“Neither Harper nor Alex is guilty.”
Parker
“Neither Marley nor Harper is guilty.”
Harper
“Kendall is guilty.”
Alex
“Parker and Harper are both innocent.”
Kendall
“Either Parker or Alex is guilty.”
Who is guilty?
Solution: Kendall
If Kendall is guilty, Kendall's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.