Do you dispute that Russia poisoned Litvinenko as well? Enemies of the Russian state just seem to be poisoned by incredibly rare substances every now and again.
Nonetheless we're getting pretty far afield. Select two incidents where any nation has killed its double-agents or whistleblowers (and I doubt there are any nations that lavish fond treatment on their double-agents in particular), and you now have evidence against that country equivalent to that upon which you declared Russia the only possible country brazen enough to carry out these two embassy attacks (assuming they were attacks).
Skripal, Litvinenko, Gorbuntsov, Perepilichnyy and others. Not two.