Vater sagt, er habe seinen Sohn erwürgt und ihn dann als vermisst gemeldet | Der Asahi Shimbun: Aktuelle Nachrichten, japanische Nachrichten und Analysen

Do we know why? 

Why do people keep asking why? Like do you need to know the reason?

Let’s see;

They were having a new baby.

He was raising a son that was not his. (Step dad)

The first son would have inherited all the properties from his grandparents.