I imagine that Russia has been involved in treacherous faking of evidence, just as Britain and America has been, yes. However, the point here is that the people claiming that they 'know' that russia was behind the attack have a track record of literally starting wars based on lies that they have deliberately created to make other nations look bad. They have specifically not followed correct protocol and so it's like a bad dream stuck on repeat.. They lie, people blindly trust them, wars happen.. Rinse and Repeat.
Yes, it is clearly possible for the Russian mafia government to be behind the attempted murder - but to blindly state that we KNOW this was the case, given the circumstances, is foolish.
Those in the west who orgasm at the thought of millions dying in wars they start (and get paid for as a result of the involvement of major weapons companies) have plenty of motive to cause such events and pin the blame on others.