At first, the Japanese police "interrogated" four of the people whose computers had been hijacked. THREE OF THEM CONFESSED. The only reason they're not behind bars now is because:
1. Even the Japanese police noticed that there was something wrong with the case. It didn't make sense that these four people were co-operating.
2. The fourth guy was savvy enough to figure out what had happened, and explain it to the police.
This kind of crap goes on all the time here. Japan is what is known as a "soft police state".
The flip-side is, the police are so dependent on the confession to secure a conviction that, and so inept at other forms of investigation, that if you have the means to resist the pressure to confess, you walk free. That's part of how the yakuza (criminal gangs) survive in this highly regulated society.