I ask because Celtic human sacrifice in ancient Britain is somewhat controversial in popular history. My impression is that historians used to assume it happened because the Romans said so, revisionist historians decided it was Roman+Christian propaganda, and now it's taken a bit more seriously because sites of ritual execution have been found. But how can historians and archeologists tell the difference between "we must sacrifice a person to please the gods" and "the Gods demand we execute this person who committed murder", when both are likely to have been killed in a ritual manner?
I would be very interested to hear what the historic discussion is over this!
I'll amplify the OP with another Roman example - the killing of prisoners after triumphs seems to also raise this question. Is that a human sacrifice, or an "execution" that happens to have strong religious elements?
A more modern comparison that also comes to mind in this question is how ritual killings in Tenochtitlan were described by Europeans at the time and afterwards as human sacrifice, but ritual killings in Europe that shared some superficial similarities (I'm specifically thinking of hanging, drawing and quartering) and were done for religious reasons/the condoning of religious authorities do not get described that way.