Case 220
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.
Kendall
“Either Marley or Reese is guilty.”
Marley
“Kendall is guilty.”
Reese
“Neither Marley nor Hayden is guilty.”
Hayden
“Neither Marley nor Reese is guilty.”
Parker
“Hayden is innocent.”
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.