More like 99.9%....

What the 99.9% Figure Actually Measures

The conviction rate tracks only cases where a prosecutor has formally indicted a defendant and brought the case to trial. It does not reflect the outcome of all police investigations, all arrests, or all cases referred to prosecutors. This distinction matters enormously. Japanese prosecutors decline to indict in roughly 60% of cases referred to them by police, meaning fewer than one in three cases that police hand off ever reaches a courtroom.1 The 99.9% applies only to that narrow slice of cases that survived the screening process.

This makes direct comparisons with other countries misleading. In the U.S. federal system, prosecutors indict more than 80% of referred cases, but over 97% of those are resolved through plea bargains where the defendant agrees to plead guilty in exchange for reduced charges or a lighter sentence. If you counted those guilty pleas as convictions the same way Japan counts trial outcomes, the U.S. federal conviction rate would also exceed 99%. The roughly 83% conviction rate Americans typically hear about applies only to contested trials. Japan has no comparable plea bargaining system for most crimes, so nearly all its cases go to a full trial, and the 99.9% figure reflects verdicts after that process.