TOKYO — Around 10:50 p.m. on the night of June 24, a very pale and thin man with glasses parked his bicycle and walked into a police station in Fukuoka City’s Higashi ward carrying a large bag. He told the police there, “I’ve killed a man.” In the bag was a seven-inch blood-stained knife. There was blood on his shoes. Later at police headquarters he would explain that he had killed a cybercrime expert who called him out as an internet troll. He admitted to taking online anger into the real world with a vengeance.

The victim, Kenichiro Okamoto, was a 41-year-old expert on cybersecurity from Tokyo who had given a lecture in Fukuoka that night that touched on how to deal with online harassment, disputes, and trolls. He was stabbed to death in the bathroom of the lecture venue about 15 minutes after he finished his presentation.

The Fukuoka Police announced early in the morning of June 25, that the alleged assailant was an unemployed local resident, 42-year-old Hidemitsu Matsumoto, who admitted he “bore a grudge” against Okamoto “because he ridiculed me on the internet.”

The late Mr. Okamoto had worked for the Tokyo-based internet security provider Sprout Inc. and was widely respected in his field. (The company posted its condolences, saying that the cyber-security world lost a very valuable person with his passing.) On his off hours Okamoto worked as a citizen journalist,posting anonymously under the pseudonym Hagex, and on his blogs “Hagex” often called out trolls for their bad behavior. Indeed, he was called by some a “troll hunter,” and part of his tactic was to troll the trolls. He sometimes added pointed critiques of what they were doing and commented on the content and quality of their writing.

Matsumoto, the suspect, had been one of Hagex’s prey.

The Grudge

Okamoto, under his pen-name, allegedly referred to Matsumoto as “Teino Sensei”— a Japan phrase meaning “Halfwit Teacher” or “Low-Intelligence Instructor.”

On May 2, Hagex wrote a self-congratulatory post with the heading, “I was surprised by how swiftly [blogging service] Hatena took action against Half-Wit Teacher.” Okamoto had pointed out that Half-Wit Teacher was using many different IDs to insult and harass other bloggers, and that Okamoto himself had reported the troll several times, so the blogging service froze the troll’s accounts within three minutes after Okamoto filed a report on May 1. He added in his post, “I think that Hatena should report Half-Wit Teacher [to the police] for forcible obstruction of business.”

That’s a very Japanese sort of offense, and the penalty for forcibly obstructing business is a hefty fine, or up to three years in prison. The freezing of Matsumoto’s blogging account and the suggestion that he be criminally charged are believed to have been motivating factors in the fatal stabbing.

The police are still investigating a blog entry posted late on June 24, after the stabbing, which they suspect was written by Matsumoto: “While laughing hysterically you called me ‘Half-Wit Teacher’ and blew the whistle on me and forced me out. Well, this is my reply to you.”

The words chosen for “shut out” (fuusatsu) literally mean “block” and “kill” and seem to convey the extreme anger of the writer, while also justifying his actions. The person posting those lines also suggested he would turn himself in to the police.

While there have been numerous cases of social networking sites in Japan being used by deranged criminals to lure people to their deaths, or attempt to do so, it’s still very rare for someone to be killed for what they wrote in cyberspace.

The First Meeting Was Their Last

Japanese media and police sources say that Matsumoto not only never met Okamoto prior to the alleged murder, he didn’t even know his real name. Matsumoto reportedly found an image of “Hagex” online. He used that and Okamoto’s blog to track him down, and he told police he waited until after the lecture to kill him.

Hagex/Okamoto wasn’t especially cautious about revealing his identity, in fact. Above the Hagex blog post about “Half-Wit Sensei” there was a link advertising where and when Okamoto, as Hagex, would be speaking in Fukuoka. Okamoto also wrote about the event in another May entry on the same blog.

Should he Okamoto have been more careful? That depends on whether you think criticism of an internet troll ever merits a death sentence. And the answer is not in a civilized society, but around the world civility, if not civilization, is on the wane.

A fellow blogger and colleague wrote after Okamoto’s his death, “He never seemed to consider that online violence would boil over into real world violence.”

One of Matsumoto’s real-world friends, an office worker who goes by the handle @DELETE_ALL on Twitter, responded to a request for comment from The Daily Beast and had this to say.

“I’m tremendously shaken and all I can really say is that this crime was terrorism. There was never [to my knowledge] any previous back and forth between the victim and the assailant. It makes me very angry to read words implying that Okamoto provoked the assailant. He was getting ready to launch his own efforts to make the internet and the cyber environment better. I was planning to co-host an event with him in which we would offer a plan to make the blogging environment even better. I am mortified.”

DELETE_ALL does not use his real name in his writings or his blogs, and after what happened to Okamoto, who can blame him?