Officials released Kitamura on October 6 after determining that Kitamura's computer was infected by a virus that allowed a third party to remotely access his PC.
The authorities arrested Kitamura in August. They had accused him of going to Osaka's inquiry page on the Internet and writing, "I will commit a massacre in Otaroad [in Osaka's Nipponbashi area] next Sunday. I will ram into pedestrian paradise, and after stabbing indiscriminately with a knife, I will commit suicide" on July 29 at about 9:45 p.m.
Source: Yahoo! Japan News via Yaraon!