Legal analysis: The investigation and evidence collection of public security cases by public security organs should be timely, objective and comprehensive. It is strictly forbidden to extort confessions by torture and to collect evidence by threats, seduction, deception or other illegal means, and it is clearly stipulated that evidence collected by illegal means will not be accepted. When investigating and handling public security cases, the public security organs may register and preserve the evidence in advance in accordance with legal procedures when the evidence may be lost or difficult to obtain later. Before closing the case, the registered evidence shall not be destroyed or transferred. There are three situations that the people's police should avoid in the process of investigating public security cases, that is, I am a party or a close relative of the party, and I or my close relatives have an interest in the case, or have other relations with the offender or the infringed person in this case, which may affect the fair handling of the case.

Legal basis: Provisions on Procedures of Public Security Organs for Handling Administrative Cases Article 28 When collecting and collecting evidence from relevant units and individuals, public security organs shall inform them that they must provide evidence truthfully, and inform them of the legal responsibilities they should bear for forging, concealing or destroying evidence and providing false testimony. Need to obtain evidence from the relevant units and individuals, with the approval of the person in charge of the case handling department of the public security organ, issue a notice of obtaining evidence, and specify the evidence obtained and the time limit for providing it. The transferee shall affix his seal or signature to the notice. If the transferee refuses, the public security organ shall indicate it. When necessary, the public security organ shall fix the content of evidence and the process of obtaining evidence by means of audio and video recording. If it is urgent to obtain evidence from the relevant units, the public security organ may inform the identity of the people's police by telephone, and send the Notice of Obtaining Evidence together with a copy of the people's police card of the people's police handling the case to the relevant units by fax or Internet communication tools.