Kenichiro Okamoto. (Video still/ANN News/YouTube)

Cybercrimes expert and prolific Japanese blogger Kenichiro Okamoto was killed over the weekend, allegedly by a man with whom police say he repeatedly clashed online.

On Sunday night, Okamoto held a two-hour seminar in Fukuoka, a city roughly 550 miles west of Tokyo, during which he talked about ways to drive website traffic and gave tips on how to deal with Internet feuds.

Blogging under the username “hagex,” Okamoto penned more than 26,000 posts on a variety of subjects. In his profile, he described the blog, which has amassed just over 1,000 followers, as the “diary of a net watcher who loves the Internet three times more than rice.” However, for many Internet celebrities, a digital platform can bring about sudden fame, and with that comes hate comments as well as other types of harassment. Okamoto was no different.

“I’ve encountered various troubles when I’ve been blogging,” he wrote in a description of the seminar, citing problems ranging from people pointing out typos to fights.

About 15 minutes after he concluded his talk, authorities say a man that had trolled and harassed Okamoto online attacked him in a men’s restroom, stabbing him repeatedly in the chest and neck, Asahi Shimbun reported. The man then fled the scene on a bicycle, according to the Japanese newspaper. Okamoto was taken to a hospital, where he was pronounced dead.

Immediately after the stabbing, a post appeared online in which the user wrote, “I am going to go now to my neighborhood police box to voluntarily surrender and take responsibility for my actions,” Mainichi Shimbun reported.

Late Sunday, a man identified as Hidemitsu Matsumoto turned himself in, saying he was “responsible for the murder in Chuo Ward,” the neighborhood where the seminar took place. A bloody knife was reportedly found in his bag, according to Mainichi Shimbun.

On Monday local time, police announced that they had arrested Matsumoto in connection with the killing.

According to Asahi Shimbun, police quoted Matsumoto saying, “I held a grudge against him over Internet (exchanges),” and “I thought I would kill him.”

While authorities say the pair never met in person, they are investigating a possible online connection, the newspaper reported.

In his blog, Okamoto wrote about his repeated encounters with an Internet troll he called “Teino Sensei,” or “Mr. Half-wit.”

On May 2, he wrote that the user had slandered him online and once harassed him seven times in one day.

“People who, like me, are accustomed to abusive phrases, do not have a problem,” he wrote. However, he noted that many other people would be scared if they were verbally attacked without warning.

Okamoto’s blog usually quoted posts from other websites along with his own commentary, and some of his posts were provocative.

However, Ryotaro Okada, president of an Internet security company, who once had been interviewed by Okamoto, told Asahi Shimbun that the blogger’s goal was to “pass on truly valuable information” to readers.

Internet trolls have become a bigger problem in Japan in recent years. According to a recent report from the country’s National Police Agency, the number of cases of online defamation and slander increased from 9,425 in 2013 to more than 11,000 in 2016.

“This incident revealed that the threat of anonymous intimidation that will result in a loss to society has become all too real,” Okada said.