Two major news outlets (~Wikipedia page + generally considered serious) is enough to count as "Western media".

Some uncertainty, but strong lean in credence, is alright for both sides (Putin / Western media).

Suggestions ~"Maybe it's fake" would not be enough, neither would more general accusations "CIA fake videos all the time".
Statement has to come from Putin explicitly, other parts of government do not count.

I won't trade in this market, as resolution is likely to get tricky.