I would recommend you begin with Sahagún's General History of the Things of New Spain or Florentine Codex. Shortly after the Spanish conquered the Aztecs, Fray Bernardino de Sahagún compiled a 12-volume ethnography, "General History of the Things of New Spain or Florentine Codex". It is one of the world’s most valuable archaeological documents, providing a stunning view into the Aztecs’ polytheistic religion. It is clear from a reading that Sahagun fully understood the Aztec god Tezcatlipoca's similarity to Satan.
Other valuable sources of information include:
Arens, W The Man-Eating Myth. New York Oxford University Press (1979)
Berdan, Francis F. (2005) The Aztecs of Central Mexico: An Imperial Society. Thomson and Wadsworth
Carrasco, David. Lindsay Jones, Scott Sessions (2000)Mesoamerica’s Classic heritage, From Teotihuacan to the Aztecs University Press of Colorado
Codex Dresden(sixteenth-Century) Codex Dresden
Codex Ixtlilxochtli( sixteeth_century)Codex Ixtlilxochtli
Codex Magliabecchiano(1970) Codex Magliabecchiano,
commentary by Ferdinand Anders. Graz: Akademische Druck-u. Verlagsanstalt (originally composed: mid-sixteenth century).
Codex Mendoza (1983) Codex Mendoza, James Cooper Clark, ed., 3 vols. London Waterlow (originally composed: ca. 1541).
Diaz del Castillo, Bernal 1956. The Discovery and Conquest of Mexico. New York: Noonday
Harner M (1977) The Ecological Basis for Aztec Sacrifice. American Ethnologist. 4:117-135
Lopez Lujan, Leonardo (2000) The Offerings of the Templo Mayor. University Press of Colorado
Leon-Portilla, Miguel. 1963. Aztec Thought and Culture. University of Oklahoma Press
Reeves, Peggy. (1986) Divine Hunger. Cambridge University Press
Sagon, Eli (1974) Cannibalism; Human Aggression and cultural Form. Harper & Row
“It is clear from a reading that Sahagun fully understood the Aztec god Tezcatlipoca’s similarity to Satan.”
Tezcatlipoca *was* Satan, but that’s not the point.
I was asking for a source for your assertion that the Spaniards didn’t regard the Indios as human.