legal ground
The Code for Lawyers' Participation in Criminal Proceedings stipulates that:
Article 26 A lawyer shall go through the following procedures when meeting a criminal suspect in custody:
(a) a special certificate issued by the law firm to meet the criminal suspect;
(2) the lawyer's own lawyer's practice certificate;
(3) Power of attorney signed by the client.
Article 27 When a lawyer meets a criminal suspect in custody, he shall solicit his opinions on the lawyer he has hired. If you agree, ask him to sign the power of attorney to hire a lawyer.