An elderly woman lived alone in her house by the suburbs. She rarely left the house and knew only a few people. One Friday morning, the mailman called out for the woman but didn’t receive a prompt answer as usual. Upon peeking in through the window, the mailman realized that the woman was murdered. The police investigated the house and found Tuesday’s newspaper by the dead body. Also, by the door outside, there were three unopened bottles of milk, one of which had gone bad.The police arrested the killer the very next day. How did they figure out so quickly?