A rich old woman lived by herself in her home in the suburbs. She rarely left her house and only knew a few people in town. One Friday morning, the mailman called the police to report that he saw her dead inside.
The police questioned the mail carrier. He explained that upon peeking through the window, he saw laying dead on the floor.
The detectives investigated the house and found Tuesday’s mail by the dead body. By the door outside there were three unopneed bottles of milk, one of which had gone bad.
The police arrested the killer the very next day. How did they solve the murder so quickly?