The lawyer's letter is usually put in the evidence file as evidence. In China, evidence volume refers to the document that collects and compiles evidence. According to the provisions of the Criminal Procedure Law of People's Republic of China (PRC), the evidence volume shall include the following contents:
Case materials, including written materials and other evidential materials provided by defendants and defenders.
Transcripts of inquiry, including confessions of defendants and defenders during the trial and other transcripts of inquiry.
Transcripts of witness testimony, including the testimony of witnesses in the trial and the testimony of other witnesses.
Expert opinions, including forensic expert opinions and technical expert opinions.
Other evidence, including video materials, audio-visual materials, etc.
Therefore, the lawyer's letter is usually attached to the evidence volume.