to kill someone treacherously, without anyone else being present (see Molina)
Alonso de Molina:
ichtacamictia. nite. (pret. oniteichtacamicti.) matar a traycion, sin que nadie este presente. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 32v. col. 1. Thanks to Joe Campbell for providing the transcription.