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.
You have not received the notice so far, because it is impossible to notify or the notice of suspected crimes or terrorist activities endangering national security may hinder the investigation.
I suggest you hire a lawyer to go to the public security organ to understand the case and meet the criminal suspect.