Recently, he wrote on his blog about being harassed by an internet troll he called “Mr. Low I.Q.”

The troll, Mr. Okamoto wrote in a May 2 blog post, slandered him in online posts, and once harassed him seven times in a single day.

Mr. Okamoto did not name the troll, but provided a list of close to 270 user names that he said the troll had used and whose accounts Hatena, a popular blogging service in Japan, had suspended at his request.

“As soon as I receive a call from Mr. Low I.Q., I report it to Hatena,” Mr. Okamoto wrote. “Initially, I used to write scrupulously: ‘This person heaps abuse on other users, including myself,’ as the reason, but these days I simply write: ‘This is by Mr. Low I.Q.’ and send it, and the account associated with it gets frozen.”

Mr. Okamoto continued, “It’s not a problem for people who are used to abusive language, like me, but a great many people would feel frightened when they receive invectives out of the blue.”

The police were not immediately able to confirm that the troll in question was Mr. Matsumoto, but several online commentators said they believed he was the troll who had been bothering Mr. Okamoto.

The killing highlighted the chilling possibility of digital threats spilling over into real life, in an era when internet users are increasingly concerned about the proliferation of misinformation, hate speech and even incitement to violence.

“The digital world is anonymous, and therefore it is easy for threats to get escalated there,” Yoh Mikami, a journalist who covers information technology, told Nishinihon Shimbun, a local newspaper. “Hatred toward people you wouldn’t meet in the real world heightens.”