Case 110
The Lost Access Card
A master access card was taken from the reception desk.
Rule: exactly one suspect is guilty. The guilty suspect lies. Every innocent suspect tells the truth.
Avery
“Harper is innocent.”
Harper
“Alex and Kai are both innocent.”
Alex
“Neither Avery nor Harper is guilty.”
Marley
“Either Avery or Harper is guilty.”
Kai
“Either Harper or Marley is guilty.”
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.