Case 318
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.
Marley
“Avery is guilty.”
Quinn
“Avery and Cameron are both innocent.”
Avery
“Marley is guilty.”
Drew
“Cameron is innocent.”
Cameron
“Drew is 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.