"Structure 10L-20 had been described by Palacio in the 16th century as a 'tower', and before its destruction by the river at the turn of this century it was partially excavated by Maudslay. His excavations revealed that the super-structure had two floors, and that the building's cord-holders (for securing the doors) were set on the outside. This placement was taken to indicate that the building was designed to be sealed from the outside, and led the Austrian architects Hasso Hohmann and Annegrette Vogrin to conclude that structure 10L-20 was a jail. Its adornment with Killer Bats, its similarity to the 'House of Bats' described in the Popol Vuh, and the Lacandon Maya custom of confining prospective victims of sacrificial rites in wooden cages all strengthen this interpretation."
William L. Fash, Scribes, Warriors and Kings: The City of Copán and the Ancient Maya, p. 130