If it were a criminal case you could be right. But you cannot sue a nation state, you cannot imprison an institution and culpable people may be hard to come by.
But actually, civil liability is more relevant here, since worldwide damages were extreme and changes in how virus research is handled are obviously necessary. So if one were to sue relevant parties in a civil court for damages or to force their procedures to be changed, the standard of proof is just "more likely than the other explanations". And I think one may get there, at some point.
Also, for a civil case, intent isn't necessary, negligence would also suffice.
But actually, civil liability is more relevant here, since worldwide damages were extreme and changes in how virus research is handled are obviously necessary. So if one were to sue relevant parties in a civil court for damages or to force their procedures to be changed, the standard of proof is just "more likely than the other explanations". And I think one may get there, at some point.
Also, for a civil case, intent isn't necessary, negligence would also suffice.