legal ground
Article 35 of the Lawyers Law
The entrusted lawyer may, according to the needs of the case, apply to the people's procuratorate or the people's court to collect and obtain evidence or apply to the people's court to notify witnesses to testify in court. If a lawyer investigates and collects evidence by himself, he may, with the lawyer's practice certificate and the certificate of the law firm, investigate the situation related to undertaking legal affairs with the relevant units or individuals.
Article 40 of the Criminal Procedure Law
From the date when the people's procuratorate examines and prosecutes the case, the defense lawyer may consult, extract and copy the case file. Other defenders may also consult, extract and copy the above materials with the permission of the people's court or the people's procuratorate.