Article 83 of the Law of People's Republic of China (PRC) on Public Security Administration Punishment stipulates that after summoning violators, public security organs shall promptly ask for verification, and the time for inquiry and verification shall not exceed eight hours; If the situation is complicated and the punishment of administrative detention can be applied according to the provisions of this law, the time for questioning and verification shall not exceed 24 hours. The public security organ shall promptly notify the family members of the summoned person of the reason and place of the summons.
If it is in violation of the Criminal Law, the law has the following provisions: Article 61 The public security organ shall produce the Certificate of Arrest and order it to sign (seal) the Certificate of Arrest and press its handprint. After the criminal suspect arrives at the case, he shall be ordered to fill in the time of arrival on the Arrest Warrant. After the end of the interrogation, the time of the end of the interrogation shall be filled in on the Arrest Certificate. If the criminal suspect refuses to fill in the form, the investigator shall indicate it on the Arrest Certificate.
Article 62 The time for summoning shall not exceed 12 hours, and consecutive summonses shall not be allowed.
Detain criminal suspects in disguise. If it is necessary to change the detained heir into other compulsory measures, it shall be approved within the detention period.
Or a decision not to approve; If it is not approved, the summons shall be terminated immediately.
So no matter what your friend's situation is, four days without any notice is illegal. You should ask the public security bureau or police station where the policeman who took him away is located!