People's Republic of China (PRC) Lawyers Law
Article 35
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 31
When acting as a defender, a lawyer shall, according to facts and laws, put forward materials and opinions on whether the criminal suspect or defendant is innocent, the crime is light or the criminal responsibility is reduced or exempted, and safeguard the litigation rights and other legitimate rights and interests of the criminal suspect or defendant.