Case 206
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
“Alex is innocent.”
Hayden
“Alex is guilty.”
Elliot
“Kai and Alex are both innocent.”
Kai
“Neither Marley nor Elliot is guilty.”
Alex
“Elliot is innocent.”
Who is guilty?
Solution: Hayden
If Hayden is guilty, Hayden's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.