"Who is The Killer?"

An eighty-year-old person was living alone in his house. On a sunny Friday morning, while delivering some letters in the mailbox, the postman felt suspicious and decided to look through the window of the house. That’s when he saw the old man lying dead on the floor in a puddle of blood. When the police arrived, they found three bottles of milk, the Tuesday’s newspaper, and some gifts in front of the house. The lock of the door was broken, and they already suspected a person.

Whom and why?

He might be the murderer! 

Little Mistake By The Murderer!

What was the incident?

The police suspected the newspaper straightaway.

Since there were 3 bottles of milk, it's clear that the old man died 3 days ago i.e. on Tuesday & milkman didn't have idea of it. Hence, he has dropped milk bottles there. 

But the newspaper boy knew that the old man is no more in this world hence he didn't drop newspaper since Wednesday.