Case 143
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.
Parker
“Either Casey or Drew is guilty.”
Casey
“Parker is guilty.”
Drew
“Either Casey or Emery is guilty.”
Emery
“Drew and Jules are both innocent.”
Jules
“Neither Drew nor Emery is guilty.”
Who is guilty?
Solution: Casey
If Casey is guilty, Casey's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.