Maniac killer in Japan

In Nayoga, Japan, a 30-year old man stabbed five members of his family with a kitchen knife, killing two of them. His brother, girlfriend and his mother were injured while his father and his niece of one years old were killed. You would not believe it but the reason for the attack was that the internet access to the family home had been cut off, presumely by the father. There are also reports that the man had confined himself to his room for the past 15-years old.
In my opinion, the man is most likely to be mentally unsound. During the past 15years that he confined himself, he probably got addicted to something online, to the point where he lost himself over it.
I feel that in order to prevent such tragedies from happening, the family members of people with high internet usage should monitor what they are doing, make sure they do not get addicted or hooked onto anything, to prevent themselves from ending up like this Japanese man.