"Fantastic job on integrating the psychiatric profile and semantic analysis, everyone. It looks like we were so accurate that we independently faked the exact same email he actually wrote!"

Arrington's exact quote, "shown an email that proved that they were the source" actually doesn't say it was an email between Arrington and the source, although I'm fairly sure that's what was meant.

Edit: To be fair, I suppose we should consider that the average guilty person isn't going to do well when confronted with specific, correct accusations, even if the evidence was faked or incorrect.