legal ground
Article 85 of the Criminal Procedure Law
When a public security organ detains a person, it must produce a detention permit.
After detention, the detained person shall be immediately sent to the detention center for custody, and shall not exceed twenty-four hours. Unless it is impossible to notify or the notification of suspected crimes endangering national security or terrorist activities may hinder the investigation, the family members of the detained person shall be notified within 24 hours after detention. After the circumstances that hinder the investigation disappear, the family members of the detained person shall be notified immediately.
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