It could be that Japan is lenient and does not prosecute cases which are not cut and dry. I don't know. Anyway I don't know how much you are helping the USA he

It could be that Japan is lenient and does not prosecute cases which are not cut and dry. I don't know. Anyway I don't know how much you are helping the USA here in your argument. A deal in the US is often like: "Look, kid. With this deal, you get 1 year in prison. If we choose to prosecute, you are looking at 30 years to life. Your call. Remember, you have a [kid|mother|girlfriend]." Who would risk going up in court, even if you maybe didn't even do very much? It's basic economics. The risk is too great that jury is going to hate you, no matter what you did or didn't do. Better take the bargain and cut your losses.