For years, Japanese police have been very poor in actual investigation skill since they almost entirely depend on interrogation leading to a signed confession. If ever arrested in Japan, don't say anything, don't sign anything. The entire game on their part is to get you to sign something saying you did it before their time limit on holding you expires.
Also, these interrogations are not required to be recorded. There have been a number of case of clearly innocent people confessing to things that may not have even happened (non-existent crimes) because they just wanted the interrogations to stop:
https://www.bbc.com/news/magazine-20810572Japan "boasted" a 99% conviction rate. This is largely due to entirely relying on "extracting" confessions rather than any sort of crime-solving prowess. Also, these interrogations have never been recorded, and the police are actively hostile to the suggestion of having interrogations recorded. But a number of high profile cases regarding false confessions have started things moving hopefully.
However there was a small victory this year. The Japanese government finally mandated recording of interviews for serious crimes, in June of this year. There have been recordings before, but it wasn't mandatory, which you all know means it will be abused.
https://www.japantimes.co.jp/news/2019/06/01/national/crime-legal/recording-interrogations-serious-cases-becomes-mandatory-japan/#.XezaofxS92U