Hidden True Crime speculated last night that it might be Mark Means leaking to Court TV, since they had in the past referred to him as an experienced criminal attorney when he appeared on a panel.
But the letter of excommunication? I immediately thought of someone in Chad's family, since it is stated that the letter arrived too late for Chad to make an appeal. Since he did not get the chance to appear before the counsel, it seems unfair on the part of the LDS, and an indication of a presumption of guilt.
Could be Prior, but he has not yet been caught leaking information, unlike Means who just cannot seem to keep his little mouth shut!