"What makes you so certain that Russia did do it? I am not saying they didn't but have not been privileged with the proof that they did."
Because that is what they do. And it has their signature all over it.
Like I say, any other explanation is not plausible. And to my simple mind, their behaviour incriminates them: why the speed to blame Britain? Why stamp ones feet and make ridiculous allegations exactly as they accuse Britain of doing - only in their case presumably without even the circumstantial evidence.
A BBC Russia reporter went there to interview Mr Skripal's niece. She was asked "If the British offered to pay for your flight to visit your uncle in hospital, would you go". And I thought: why does the Russian government not offer to do this: after all, here is a Russian citizen (Yulya) gravely ill in hospital? Surely the least they could do, if they really are an innocent party, is to send the relatives over. Intead they demand "consular access", despite the fact that that traditionally is for citizens who have transgressed abroad.