By Mariko Oi
Japan has a conviction rate of more than 99%. But in recent months there has been a public outcry over a number of wrongful arrests where innocent people confessed to crimes.
It started with a threat posted on the city of Yokohama's website in late June: "I'll attack a primary school and kill all the children before the summer."
In the months that followed, there were a number of similar threats posted on the internet - some threatening famous people, including the Emperor's grandchildren.
After a police investigation, four people were arrested. Two, including a 19-year-old student, confessed while in custody.
But on 9 October, the real perpetrator sent an email to a lawyer - Yoji Ochiai - and local media, explaining how he or she made those threats by taking control of innocent internet users' computers with a virus.
His or her purpose, as stated in the email to Ochiai, was "to expose the police and prosecutors' abomination".
And in a way, it did. It raised the question - why did the innocent people confess to a crime that they didn't commit? What kind of pressure were they put under?
"I was surprised to have received the email but I wasn't surprised that the innocent people confessed," says Ochiai.
There have been a number of wrongful convictions in the past, he says.
"But unlike other cases, the fact that these cyber threat incidents happened to ordinary people who were just using the internet raised the fear that it could have happened to anyone," he adds.