A man is found murdered on a Sunday morning. His wife calls the police, who question the wife and the staff, and are given the following alibis: (1) The wife says she was sleeping. (2) The butler was cleaning the closet. (3) The gardener was picking vegetables. (4) The maid was getting the mail. (5) The cook was preparing breakfast. Immediately, the police arrest the murderer. Who did it, and how did the police know?
The mail doesn’t come on Sundays, so the maid is guilty.