I think most people who have studied de Rais in any depth have run across (very) occasional claims for his innocence. To be perfectly frank, proponents of this view are treated with the same disdain as holocaust deniers. No, I don't find anecdotal reference to a report that a near contemporary of de Rais entertained doubts as to his guilt at all "interesting." De Rais was a Marshall of France, after all, there were bound to be some who could not countenance the idea that he was capable of such crimes. And as for that book on Béla Bartók you allude to in support of the man's innocence—whose title you cannot even remember—how marginal and tangential can a publication be to the case of de Rais than a (putative) book on Bartók?!?.