What's the opposite of the "Big Lie"

"A big lie (German: große Lüge) is a propaganda technique. The expression was coined by Adolf Hitler, when he dictated his 1925 book Mein Kampf, about the use of a lie so "colossal" that no one would believe that someone "could have the impudence to distort the truth so infamously""

What is it called when something evil was perpetrated by someone who was supposed to be benevolent, but it is not believed by the masses because it was so incredibly egregious that their cover-up lies are more believed than what actually took place?