Relevant U.S. laws give lawyers the right to investigate and obtain evidence

The Sixth Amendment to the U.S. Constitution provides that defendants have the right to hire an attorney to defend themselves. In judicial practice, this guarantee is understood to mean that defendants can be represented by lawyers at every important stage of criminal proceedings. Its purpose is to ensure that the legitimate rights and interests of criminal defendants are not violated at all stages of criminal proceedings and to ensure that the court can achieve a fair trial. If the defendant is poor and cannot afford a lawyer, the court is obliged to appoint a lawyer at the government's expense. Failure to grant or guarantee this right to a defendant at trial, when the defendant pleads guilty, or at sentencing constitutes a significant infringement of constitutional rights, with the consequence that any verdict convicting the defendant will automatically be quashed.

The U.S. Federal Rules of Civil Procedure stipulates that in the evidence discovery procedure, parties have five methods to collect evidence materials: (1) Deposition, which refers to the deposition by one party after the oath is taken. The procedure and method by which the court clerk takes evidence from witnesses in the presence of both parties and their attorneys. (ii) Interrogation refers to the procedure and method in which one party interrogates the other party in writing and requires the other party to answer. (3) Request for production of documents and other things refers to the procedure and method for one party to request the other party and anyone else to provide documents and other physical objects in its possession or control. (4) Request for Admission refers to the procedure and method by which one party requests the other party to express its opinion on the facts of the case, whether the document is established, the litigation claims and the application of the law, and to express its attitude of recognition of the other party. (5) Identity and mental examination (Physical and mental examination) refers to the procedures and methods by which one party can require the other party or the person under its protection and control to undergo a physical or mental examination.