Russian leadership obviously does not believe it is true. No one in their right mind would believe it, and, in any case, they are prove pathological liars and killers.
Putin has been stating his position on this topic publicly for years/decades actually.
He has reasons for that view—there is nothing unreasonable about drawing that conclusion.
It is not reasonable to claim that anyone who disagrees with you on a debatable proposition is a “pathological liar”.