Because banishment from a community was a basic punishment in the Edo period, the communities of criminals who had been banished from authorized communities such as towns and villages were built outside of there, so criminal investigations themselves were difficult without hiring people who knew much about the inner societies.
江戸時代の刑罰は共同体からの追放刑が基本であったため、町や村といった公認された共同体の外部に、そこからの追放を受けた犯罪者の共同体が形成され、その内部社会に通じた者を使わなければ犯罪捜査自体が困難だったのである。