A long time before the crash of the Byzantium, a man called Rastan Jovanich wrote the definitive work on Weeping Angels, presumably as a warning to others. It is unknown how Jovanich gained this information, though possession of the knowledge eventually drove him mad. The people of his time sent him to a "terrible" sanatorium. (WC: Monster Files: Weeping Angels) The Doctor kept the book and eventually stored it in the TARDIS drawing room. (GAME: TARDIS)