The suspect reportedly harassed the victim online before the attack, even though the two had never met in person.

An expert on internet crime and prominent blogger was stabbed to death in Japan after giving a seminar on dealing with internet trolls, allegedly by a man who had reportedly harassed him online.

Kenichiro Okamoto died Sunday after holding a two-hour seminar for about 30 people in the city of Fukuoka, about 550 miles west of Tokyo, The New York Times reported Tuesday. The seminar aimed to advise bloggers about engaging with their audience and how to handle trolls.

“I have encountered many troubles as I have written my blog for many years,” Okamoto wrote on a website introducing the seminar. “Quarrels, pointing out typos, questions about the content, love letters, letters from attorneys, etc.”

Fifteen minutes after the seminar ended, Okamoto entered a men’s room in the building where the seminar was held, where he was stabbed several times in the neck and chest, The Times reported. He was taken to a hospital, where he was declared dead.

Hidemitsu Matsumoto, the 42-year-old suspect in the killing, fled the scene but surrendered to police a few hours later, the Japanese newspaper Asahi Shimbun reported. Matsumoto had never met Okamoto in person but had harassed Okamoto online and “held a grudge” against Okamoto, the newspaper reported.

The killing underscores the danger of violence erupting in the real world from the practice of deliberately provoking, demeaning and threatening others online. Over the past few years in particular, social media sites such as Facebook and Twitter have become a central stage for abuse including revenge porn, attack mobs, privacy violations and death threats.

The phenomenon of swatting, anonymous reports of fake hostage situations, shootings and other violent crimes, has become a popular form of harassment in recent years, particularly among online gamers and hackers. The FBI estimates that roughly 400 cases of swatting occur annually.

The FBI believes the death of an unarmed man in Kansas last year may have been the result of a swatting that arose from an argument between two players of an online game. Security researcher Brian Krebs, himself a former swatting victim, tracked down the alleged parties of the dispute on Twitter.

Read more at CNet.