White Paper on Crime 2019 Part2/Chapter2
Judicial police officials are to refer every criminal case to public prosecutors, except cases subject to disposition as trivial offenses (certain minor offenses with particularly strong mitigating factors that satisfy public prosecutor’s predesignated criteria are not required to be referred to public prosecutors pursuant to the proviso to Article 246 of the Code of Criminal Procedure) and certain violations of the Road Traffic Act that are subject to Hansokukin (administrative fine).
Public prosecutors investigate cases referred by the police or other special judicial police officials (officials of investigative agencies other than the police, who have specific jurisdiction; e.g. coast guard officers, narcotics agents, etc.). In addition, where necessary, public prosecutors may institute an investigation on their own initiative or in response to a complaint or accusation directed to the office. In concluding the investigation, they decide whether or not to prosecute the suspect, based on factors such as whether or not his/her act constitutes an offense and if the act requires punishment.