Legal basis: Article 175th of the Criminal Procedure Law of People's Republic of China (PRC). When examining a case, the people's procuratorate may request the public security organ to provide evidence materials necessary for the trial. If he thinks that there may be cases of collecting evidence by illegal means as stipulated in Article 56 of this Law, he may be required to explain the legality of collecting evidence. When examining a case, the people's procuratorate may return it to the public security organ for supplementary investigation or conduct its own investigation. A case under supplementary investigation shall be completed within one month. Supplementary investigation is limited to two times. After the supplementary investigation is transferred to the people's procuratorate, the people's procuratorate recalculates the time limit for examination and prosecution. If the people's procuratorate still believes that the evidence is insufficient and does not meet the conditions for prosecution in the case of the second supplementary investigation, it shall make a decision not to prosecute.