We almost surely will never have 100% proof. It's most likely a lab incident but if that is indeed the case, the proof has almost certainly already been destroyed.. <b>Maybe</b> in 30-60 years someone will leak an obscure document from Chinese government archives that proves it, or <b>maybe</b> if the US was actually involvement with funding of it, which seems unlikely, evidence could come out there. But those are about the only 2 plausible ways of getting any sort of proof.