An old man lives alone in a flat. Because of his old age, he is not able to move comfortably and hence most of the things are delivered to his home.
On Friday while delivering the mail, the postman felt something suspicious in the flat and tried to look inside through the key hole and he saw a blood filled body of the old man.
The police arrived at the scene. On the outside of flat they found two bottles of warm milk, Tuesday newspaper, some unopened mails and some gifts.
Who killed the old man and how did the police know who to arrest?
The newspaper delivery man was the murderer as the Wednesday and Thursday newspapers were missing. This indicates that he already knew that there is no one to read it.