They're were key moments that he visibly became tense. Those moments hinged around why he has not charged anyone with the underlying crime of revealing Plame's classifed status. I'm convinced he's intensely aware of the weakness of his overall investigation. He may be able to prove Libby misled the jury, but he's sensitive to the lack of evidence on Plame's status and outing.
Fritz has just admitted he does not know if Libby intentionally knew he was outing Plame!!!!!!!!!!!!!!