The flow of criminal cases is the investigation stage, the prosecution stage and the trial stage. In the investigation stage, the public security organs extract evidence and investigate relevant facts; At this stage, the law does not stipulate a specific time, but the detention of criminal suspects cannot exceed 7 months. In the review stage, the procuratorate will review the evidence of the Public Security Bureau. If it is not sufficient, the procuratorate will return it to the public security bureau for re-investigation. The time is 30 days, and it will be extended after approval.