Police grudge behind Japan hacker campaign

A computer hacker who taunted Japanese police for months with a string of vexing cyber riddles launched the campaign as part of a grudge against authorities, media reports said Tuesday.

After cracking a set of riddles, police in Tokyo reportedly found a digital memory card attached to a cat's collar which revealed a message saying "a past experience in a criminal case" had caused the hacker to act.

The message said the case "changed" the anonymous hacker's life, and added that "no more messages will be sent", Jiji Press news agency and other media reported.

The note may bring to a close a bizarre investigation which has seen threats against a number of venues—including a school and a kindergarten attended by grandchildren of Emperor Akihito—sent from computers around the country.

The National Police Agency (NPA) was embarrassed after it emerged that officers had extracted "confessions" from four people who had nothing to do with the threats.

Police held one of the suspects for several weeks before a broadcaster and lawyer received another anonymous message containing information that could only have been known by the real culprit.

The four were released as the NPA chief made a humiliating climbdown, acknowledging police had been the victims of a hacker and promising his cyber-crime unit would brush up its skills.