Case 231
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.
Avery
“Neither Logan nor Blake is guilty.”
Logan
“Alex is innocent.”
Alex
“Either Logan or Kai is guilty.”
Kai
“Either Avery or Alex is guilty.”
Blake
“Either Avery or Kai is guilty.”
Who is guilty?
Solution: Kai
If Kai is guilty, Kai's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.