The headline shall be like "A Japanese person was killed by mentally unstable person". No more than that. The killer was infamous for spamming abusive words to

The headline shall be like "A Japanese person was killed by mentally unstable person". No more than that. The killer was infamous for spamming abusive words to anybody on the Hatena Bookmark(an online bookmark service like reddit or HN), among the many abusive words he used, somehow he always use 低能(teinou, low-intelligence) so he was called 低能先生(teinou-sensei). He blamed others for no reason. He probably spamming everybody commented on popular articles. So he was suspected to have some mental issues. Everybody immediately reported him for abusing and Hatena ban his accounts as soon as they found his another accounts. The victim was a famous blogger. He was an old time "net-watcher"(a person who find funny people on the internet). He mostly deal with those who intentionally cause self-flaming on the internet for pageview or pyramid-scheme. Once he mentioned about the existence of this infamous abuser, teinou-sensei, on this "net-watching" blog. He also hosted a event on Fukuoka and it so happens that this mentally-unstable killer was lived in Fukuoka. The connection of his "net-watcher" persona and cyber-security expert part of his life wasn't known beforehand of his death. You can't get any moral from this incident. It's just there are mentally unstable people in the world and many abusers on the internet are probably those people.