[J]udges rely excessively on ... depositions, especially in cases handled by special investigation squads, which exist only at the district public prosecutors offices in Tokyo, Osaka and Nagoya. Thus, investigators in these special investigation squads have gotten the idea that as long as they manage to get a suspect to sign a deposition, courts will find him or her guilty. This presumption has led to unethical, and sometimes illegal, means of obtaining confessions.
This partly explains why 99.9 percent of defendants in criminal cases are found guilty and why the process has become a hothouse for generating false charges.
Another problem with criminal court proceedings at present is that public prosecutors present only the "best evidence" to courts. They select the testimony and material evidence that they find useful in winning conviction. Since prosecutors don't have to disclose testimony or evidence favorable to a defendant, it is only natural that they normally succeed in getting a conviction.
It's the job of defense lawyers to find evidence favorable to defendants. Even if they find such evidence, if it has not been disclosed by the prosecution, they must obtain the Supreme Court's approval for presenting it to a court. The process for getting approval is complex and difficult.
The dynamic evidence page
It's here: the law of evidence on Spindle Law. See also this post and this post.