On August 9, 1765, the wooden crucifix on a bridge in Abbeville was vandalized. The bishop of Amiens is said to have roused the ire of the faithful and asked churchgoers to reveal all they could about the case to the civilian judges, under pain of excommunication. Nobody actually revealed anything about the vandalism itself, but Du Maisniel de Belleval, a local judge who had quarreled with young La Barre, gathered damaging evidence against a group of friends (possibly not realizing his own son was part of the group). Three young men, Gaillard d'Etallonde, Jean-François de La Barre, and Moisnel were accused of not having removed their hats when a procession had passed, but numerous other blasphemies were revealed was well. La Barre's bedroom was searched and among his (mainly pornographic) prohibited books, Voltaire's Philosophical Dictionary was found - providing a pretext to blame the Philosophers for the young men's misbehavior. Once the charges were put forth by the courts, one of the youths fled to Holland, and one was only 15 and simply fined; only the 19 year old La Barre remained.
Voltaire, at first horrified by the attention the affair drew to him, ended up defending La Barre's memory and helping d'Etallonde. The sentence was reversed by the National Convention during the French Revolution in 1794. Voltaire helped to make the case of the Chevalier into a cause célèbre, calling it 'this sentence so execrable, and at the same time so absurd, which is an eternal disgrace to France'.