Dante asks the librarian and the properitor of Wild Goose inn, if they know/have any books concerning Gille de Rais, specifically - the place of his demise by Ecclestian Order.
Smaug - Hoarding Plots since Hobbit.
That is the only reference he finds in the library.
In the future, there are two simple rules to remember:
DO NOT CROSS MISTER MOLOCH.