Case 184
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.
Logan
“Marley is guilty.”
Hayden
“Rowan is innocent.”
Avery
“Neither Logan nor Hayden is guilty.”
Marley
“Either Hayden or Rowan is guilty.”
Rowan
“Logan and Hayden are both innocent.”
Who is guilty?
Solution: Marley
If Marley is guilty, Marley's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.