Case 365
The Swapped Envelope
A sealed envelope was replaced with an empty one.
Rule: exactly one suspect is guilty. The guilty suspect lies. Every innocent suspect tells the truth.
Emery
“Marley and Dakota are both innocent.”
Riley
“Neither Emery nor Marley is guilty.”
Rowan
“Either Emery or Dakota is guilty.”
Marley
“Either Riley or Rowan is guilty.”
Dakota
“Neither Riley nor Marley is guilty.”
Who is guilty?
Solution: Rowan
If Rowan is guilty, Rowan's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.