|Joseph, comte de Solar, engraving by Lemoine|
Cazeaux was duly arrested, taken to Paris and thrown into a dungeon. The identity of the abbé de l'Épée's pupil seemed established for, like the original Joseph, he had an extra tooth in his upper jaw. Yet Cazeaux protested his innocence and, before his trial, the famous lawyer Élie de Beaumont, defender of Jean Calas, produced a sensational defence; Cazeaux was known to have left Toulouse on September 4th 1773 by which date "Joseph" had already been committed to Bicêtre, having been discovered in Picardy the month before. Cazeaux's lawyers protested bitterly that his arrest was based only on the abbé de l'Épée's interpretation of signing.
Cazeaux's release was followed by an investigation in Toulouse with Joseph present. The child which Cazeaux had buried was exhumed and found to be aged 8-10 years, with the same extra tooth. The judges arrived at the extraordinary verdict that Cazeaux was innocent but that the deaf boy was indeed the comte de Solar. However, in 1791 Cazeaux and Joseph's sister Caroline, who stood to lose her inheritance, successfully appealed the decision and "Joseph" was finally discredited.
The episode was the subject of a play by Jean-Nicolas Bouilly, The abbé de l'Épée, which opened in at the Comédie-Française in December 1799 and enjoyed a success second only to the Marriage of Figaro itself. The play was revived at Gallaudet University Theatre in Washington in 2011. There have been a couple of TV dramas, one by the BBC in 1991 and in 2006 a Franco-Belgian production, L'enfant du secret by Serge Meynard, both of which featured a deaf lead actor.
Excerpt from "The Count of Solar", TV film by Tristram Powell, BBC 1991 (on Vimeo):
This account is taken mostly from:
Nicholas Mirzoeff, "Signs and citizens: sign language and visual sign in the French Revolution" in The consumption of culture 1600-1800 (2013), p.283-4. Extracts on Google Books: http://books.google.co.uk/books?id=-U7bAAAAQBAJ&q=cazeaux#v=snippet&q=cazeaux&f=false
I can't find any footage from L'enfant du secret (2006): YouTube has an interview with the lead actor: https://www.youtube.com/watch?v=_Tiq2SJ8KZ0