An email was sent to media organizations and lawyers on Friday, in which the unidentified sender claimed to the be "the real culprit" behind a series of email death threats in 2012 that were sent by hacking into other people's computers.
In the high-profile case, four individuals were mistakenly arrested during the initial investigation.
Following an exhaustive hunt that at one stage had authorities tracking down a cat for clues, according to reports, IT worker Yusuke Katayama was arrested on charges of using a remote computer and sending a mass-killing threat to a comic book event after months of evading investigators with a series of vexing cyber-riddles.
Friday's email came as Katayama's trial continued Friday, Fuji TV reported. In it, the sender referred to the "PC remote control virus case," and said: "I am the one responsible. It has been a while hasn't it?" The unknown sender wrote that he/she had framed Katayama for the cyberattacks. "Katayama sure has landed in a tough spot, and I felt a bit sorry for him," the sender wrote.
The case has proved embarrassing for the National Police Agency (NPA) after it emerged that officers had extracted "confessions" from four people who had nothing to do with the threats.
An anonymous hacker then sent messages to newspapers and broadcasters, with the sender claiming details of a computer virus used to dispatch the threats were strapped to a cat living on an island near Tokyo.
After cracking a set of riddles, police found the cat and removed a digital memory card from its collar which revealed a message saying "a past experience in a criminal case" had caused the hacker to act.
Police analyzed the memory card and footage taken by security cameras, coming to suspect that Katayama, a resident of Tokyo, was responsible for the hacking campaign, media said.
Following Friday's new revelations, police said they are trying to track down the sender of the latest email and will question Katayama further, Fuji TV reported. Katayama is currently out on bail for the duration of his trial which began in February.
Katayama told a news conference Friday that he did not send the email and maintained his innocence in the case.© Japan Today/AFP