.

Schoolshoe:
A lonely old man lived in his house in the suburb of a city. He never left the house for long. It was a midsummer Friday when the mailman walked by and called out for the man. There was no answer. The mailman looked into the window and saw him in a pool of blood. When the policeman arrived, he found Tuesday’s newspaper, 2 bottles of warm milk, and 1 bottle of cold milk.

The next day, the killer was arrested. How did the police find out who it was so quickly?

The old man doesn't leave his house, which means most things are delivered to him at home.

Now, his murder was discovered on Friday and a Tuesday newspaper was found in his house. So what happened to Wed, Thur and Fri newspapers? Whoever used to deliver the newspapers must be a prime suspect. Niggah stopped showing up after killing the old man.

That is what I think though.

so many details are missing....
pool of blood could result from gunshot, stabbing or sucide( wrist slashing)
no mention of crime weapon found on the scene.

was the door locked from inside or outside

when did the man die exactly. if he had died much earlier (Tuesday) the pool of blood would have caked and the smell would have got to the mail man first.... but from the description it seems the blood was still fresh....
I suggest an autopsy should be carried out to determine his last meal