I think "both sides" have to hide a lot. These viruses have a long history, starting in Plum Island. If the US presses too hard by releasing material about the Chinese involvement, the Chinese would counter with material that shows that they just continued the work of Ft. Detrick, and that the research was paid by CIA and Pentagon (e.g. through the EcoHealth alliance that paid the Wuhan lab and got Pentagon money). US and China will find an equilibrium of accusations without releasing too much proof.