Robert Parry is a highly respected journalist. Btw, the only proof the US has presented so far has been provided by the Ukraine government and consists of social media which is highly malleable and very easily manipulated. Read the transcript of this briefing: Zero Evidence from a highly based source.
Is this your "verified source"?

This is a false flag operation to vilify Russia and the separatists. It has an underlying agenda that has nothing to do with democracy in Ukraine. Recall the intelligence on Iraq weapons of mass destruction? It was false in tell used to get us into an ill advised war. Obviously the government can't be trusted when they say they have intelligence unless they present it.