Japanese police have a reputation of "interrogating" you until you confess, regardless of innocence. That's the only way to hit their 99% conviction rate.
I think this conviction rate statistic is out of context. In the US the conviction rate is 93% and, if the US measured conviction rate the way the Japanese do, it would be 99.8%.
Forced confessions are unfortunately not unique to Japan [1]. Police will behave like that when you reward them based on the number of convictions and don't hold them accountable for screwing over innocent people.
The last thing they need is another bludgeon.