paper: 'Why Is the Japanese Conviction Rate So High?'
"Conviction rates are high in Japan. Why? We suggest it is because Japanese prosecutors are understaffed. If they can afford to bring only their strongest cases, judges see only the most obviously guilty defendants, and high conviction rates would then follow. [...]"
http://works.bepress.com/rasmusen/10/
"Download the Paper" works for me, but Google can find other copies.