Proceedure for approval of criminal background check for permanent residence visa

A friend who was born in China but now a US citizen has been working in China for 10 years. He is now applying for a permanent residence visa & asked me to get his criminal background check from when he lived in the US & send it to the Chinese authorities in the US for approval. I have the notarized document but do not know where or who to send it to. The Chinese Embassy in DC refers me to the Visa office & the Visa office never answers the phone. If you have any info or ideas concerning this matter, I would be most grateful.