History

I remember reading somewhere (Wikipedia, maybe?) that the Soviets became aware of the invasion plans before it happened by a German communist in the Wehrmacht who defected and told them about Germany's impending invasion. The article claimed the authorities disbelieved him, assumed he was a spy, and quietly executed him.

All of which sounds like something an anticommunist would make up to smear the USSR and so I'm hesitant to believe it.

Another claim I've heard was that when the invasion began Stalin didn't believe the officials telling him the Nazis were invading and thought it was a hoax and that they were conspiring against him, even threatening them. I don't remember where I heard this one but I believe it was coming from a liberal I was arguing with.

This also sounds too much like bullshit to be believable, so I'm here looking to fact check this stuff. Is there any truth to this stuff or is it just more anti-Soviet nonsense invented to make them look bad?