Missing the point
An awful lot of commentards seem to be missing the point of this story.
Thomas has never disputed that what he did was wrong, and would be grounds for a civil lawsuit from his ex employer, however, he was very specifically charged with a criminal act under the following:
"intentionally causing damage without authorization , to a protected computer."
His argument is that he should not have been charged under that statute, as he was authorised to access the computer(s) in question.
As a shaky analogy, If I cause a road accident by throwing a concrete block off a bridge, and then got charged for "driving without due care and attention" I would be within my rights to appeal, as I wasn't driving at the time.