A comparison is not relevant. The threshold is whether or not the person making the claim knew, independent of anything anyone else in the world does or doesn't know, and the burden is on the other side to prove that they did.
That's a little reductive. If that were so, there'd barely be a need for defense in our criminal system, just "Ladies and gentlemen of the jury, you've heard the prosecution's case - do you believe they've established guilt?". Instead, regardless of the ostensible burden, statements like this by the defense work to erode any claims of "beyond reasonable doubt".
You're conflating the civil and criminal judicial systems when the reality is they're quite separate, and defamation has its own special corner of the civil realm where plaintiffs have a very steep hill to climb.