Evidence preservation refers to the measures taken by the people's court to protect the evidence in order to ensure its probative force when the evidence may be damaged, lost or difficult to obtain in the future. Public security cases refer to cases constituted by acts violating public security administration. According to the Law of People's Republic of China (PRC) on Public Security Administration Punishment, the violation of public security administration must be (1) minor enough for criminal punishment. If the circumstances are serious enough to be punished by criminal law, it shall be dealt with according to criminal law. (2) Acts that should be punished according to regulations.

Legal basis:

Article 27 of the Procedures for Handling Administrative Cases by Public Security Organs: Public security organs must collect evidence that can prove whether the suspect is illegal or not and the seriousness of the illegal case in accordance with legal procedures.

It is strictly forbidden to extort confessions by torture and collect evidence by threats, deception and other illegal methods. The statements and defenses of illegal suspects collected by illegal methods such as extorting confessions by torture, statements and other witness testimonies collected by illegal methods such as violence and threats cannot be used as the basis for finalizing the case. If the collection of material evidence and documentary evidence does not conform to legal procedures and may seriously affect the justice of law enforcement, it shall be corrected or given a reasonable explanation; If it cannot be corrected or given a reasonable explanation, it cannot be used as the basis for finalizing the case.

Article 28 of the Procedures for Handling Administrative Cases by Public Security Organs: 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 their legal responsibilities 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.

Article 29 of the Procedures for Handling Administrative Cases by Public Security Organs: The physical evidence collected and retrieved shall be the original. When the original is inconvenient to carry, difficult to preserve, or should be preserved, processed or returned by the relevant departments according to law, you can take or make photos or videos that can reflect the form or content of the original.

Article 88 of the Procedures for Handling Administrative Cases by Public Security Organs: Public security organs should provide necessary conditions for appraisal, send relevant inspection materials, comparison samples and other original materials in time, introduce the situation related to appraisal, and clearly put forward the problems that need to be solved by appraisal.

The people's police handling the case shall do a good job in the storage and inspection of materials, and designate a special person to be responsible for the inspection of materials to ensure the identity and non-pollution of materials in the circulation process.

It is forbidden to force or imply an appraiser to make an appraisal opinion.