Who is Dr. Xia from Death of a Red Heroine and what is their importance?

Dr. Xia is the police medical examiner. He performs the autopsy on Guan's body and, at Chen's request, prepares a more thorough study of her, including the contents of her stomach. This leads to the discovery of caviar in her stomach, consumed not long before her death which is an important lead in the case. Xia is a fan of Chen's poetry and thinks Chen is also a good cop. He goes out of his way to show support for Chen when things get rough.