What do you mean no first hand sources? I thought those were the the eyewitness that he dismissed because some of them hadn't talked to people about their traumatic experiences before talking to the UN.

I'm not bothered by the translations. An office translation would need to be by China, right? So they'd have a motive to mistranslate to downplay what they're doing. As long as the original documents as well as the translations are available, it should be easy enough to check the translation accuracy.