Case 195
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 and Parker are both innocent.”
Reese
“Either Marley or Parker is guilty.”
Avery
“Marley is innocent.”
Parker
“Either Marley or Reese is guilty.”
Sam
“Either Reese or Parker is guilty.”
Who is guilty?
Solution: Reese
If Reese is guilty, Reese's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.