Case 292
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.
Elliot
“Either Cameron or Avery is guilty.”
Cameron
“Neither Elliot nor Casey is guilty.”
Casey
“Elliot is innocent.”
Logan
“Either Elliot or Avery is guilty.”
Avery
“Casey is guilty.”
Who is guilty?
Solution: Avery
If Avery is guilty, Avery's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.