Well, P(ukraine blames russia | russia did it) = P(ukraine blames russia | ukraine did it) = 1. But P(ukraine blames russia | nobody did anything) < 1. So Ukrai

Well, P(ukraine blames russia | russia did it) = P(ukraine blames russia | ukraine did it) = 1. But P(ukraine blames russia | nobody did anything) < 1. So Ukraine saying Russia did something still provides information that something happened. This particular piece of information might not inform whether Ukraine or Russia did it, but that doesn't mean the likelihood of the two events are equal. There are other pieces of information out there.