I think he is shaken and frightened. We can only speculate how far the corrupt FBI has gone to keep the truth from us. The changing timeline was a signal to us that the truth was being covered up. It was a signal telling us facts are being manipulated. The FBI caught on and most likely threatened the sherif. The certain truth we know about federal investigations is that they are always corrupt.
Hmm, I, too, thought “frightened” when he was speaking.