Apparently there is a void in the Imperial records regarding the origins of the chapter of the Blood Ravens. For this reason, many believe that the Blood Ravens have a very dark past and have committed such atrocities that the Empire purposely deleted some of the archives. This is a theory many heretics believe and although it's probably heretic-made filth, it hasn't been disproved. In fact the complete absence of any kind of data reinforces this theory.
Is there any historical evidence that supports this theory? Could the Empire go as far as to delete the Blood Raven's early records?
Due to the higher than normal proportion of Librarians, the colour of their armour,and their heraldry, there has been speculation that the Blood Ravens are descended from the Corvidae Cult of the Thousand Sons Traitor Legion, who were sent away prior to the VI Legion's burning of Prospero, and thus never followed their Primarch into heresy, much like the Knights-Errant who hailed from the other Traitor Legions. However, this is just speculation based on observation and any records that may have served as evidence have been suppressed or destroyed.