An old man lives alone in a flat

An old man lives alone in a flat. Because of his age , he is not able to move comfortably and hence most of the things used to be delivered to his house.

On Friday while delivering the mail , postman feels something suspicious in the flat and tries to look inside through the key hole and he saw a blood filled body of the old man.

CID arrived the scene.
On the outside of flat , he found two bottles of warm milk , Tuesday newspaper, some unopened mails , some gifts.

CID waste no time to find the murderer.

Who was the murderer ?

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Newspaper delivery man was the murderer because of absence of Wednesday and Thursday missing newspaper.
This indicates he already know that there is no one to read it.