On Sunday night, cyber-security expert and prolific blogger Kenichiro Okamoto held a seminar in the city of Fukuoka about writing on the internet. During the two-hour event, Okamoto — who also used the online handle Hagex — offered tips on how to get traffic, as well as how to deal with the “blog trouble” he had experienced online over the years, from readers pointing out typos to legal threats and internet feuds.

After the seminar, Okamoto went to the use the bathroom and was stabbed to death by an assailant, who then fled. According to The Asahi Shimbun, police say that a 42-year-old man named Hidemitsu Matsumoto later turned himself in, saying he “held a grudge” against Okamoto because of their online exchanges and had decided to kill him.