It's clear that you don't understand how logic actually works. The burden of evidence lies with the claimant. This means the onus is on Russia to prove her claim, and nobody is under any obligation top accept it until it's substantiated.
This is completely different to 'absence of evidence is not evidence of absence', which refers to something else entirely. Please, don't use technical terms unless you understand them.
Pretty sure the UK claimed first... nor have we substantiated anything either, it just seems like two children fighting honestly, which doesn't seem too surreal with Boris at the helm of it.