FUKUOKA -- Police believe Hidemitsu Matsumoto, suspected in the June 24 murder of internet security consultant and "dark web" cybercrime expert Kenichiro Okamoto, may have stated online that he had "graduated from being just a keyboard warrior" shortly before turning himself in, investigative sources told the Mainichi Shimbun.
Prefectural police sources also revealed that Okamoto, 41, had wounds in his back as well as in the front of his body, suggesting his attacker had continued to chase and stab him as he tried to flee.
Okamoto, a Tokyo-based internet security consultancy employee, was stabbed to death in Fukuoka's Chuo Ward at about 8 p.m., around 15 minutes after finishing a seminar presentation at Fukuoka Growth Next, a public-private facility to support startup companies. He was apparently attacked in a washroom on the same floor as the seminar room.
Investigators said that Matsumoto, 42, of Fukuoka's Higashi Ward, turned himself in at a police box at about 10:50 p.m. and told officers there, "I am responsible for the murder in Chuo Ward." A bloody knife was found inside his bag. He was formally arrested on June 25.
According to police, an anonymous user posted the "keyboard warrior" message on an internet bulletin board about 20 minutes before Matsumoto appeared at the police box. "Keyboard warrior" refers to internet users who only voice strong opinions online, and the post continued, "This is my reply to all you people who called me 'imbecile Sensei (teacher)' and laughed at me as you reported me and suppressed my words." The post ended, "I'm going to surrender myself at a nearby police box now and take responsibility."
Police believe Matsumoto may be the anonymous poster behind the message, and are carefully examining the details.
Okamoto and Matsumoto had apparently never met in person, but investigators have confirmed interactions between Okamoto's online handle "hagex" and Matsumoto's suspected online name "Sensei." According to a man in his 40s who says he has conversed with both men online, "Sensei" often trolled other users, calling them "imbecile" and "garbage," leading others online to start calling the user "imbecile Sensei."
Furthermore, Okamoto's "hagex" reported problem posts to site administrators, and it is believed that "Sensei" bore a grudge against the internet security specialist. The man in his 40s told the Mainichi, "There were several people 'Sensei' said he wanted to kill," but "'Sensei' never brought up hagex's name like that."
Meanwhile, investigative sources revealed to the Mainichi that Matsumoto arrived in the Fukuoka Growth Next facility area at about 4:40 p.m. on June 24, some three hours before Okamoto was killed. Police believe that the suspect may have been waiting attentively for a chance to attack the IT specialist.
(Japanese original by Makoto Kakizaki and Kenta Miyahara, Fukuoka News Department)