Of necessity, foreign policy is not conducted on the basis of incontrovertible scientific or legal certainty. It is conducted based on rational assessment of risks and the proper analysis of the available evidence in order to arrive at a balanced conclusion. The only rational conclusion in this instance - which you clearly share, btw - is that the Russian state is culpable for the attack in Salisbury.
like WMD
Northern Monkey ... who can't upload a bleeding Avatar