Well...repectfully killed. Archeological Stockholm syndrome.....
My thought is that they with held food from the victims for a few days and fed them with something that had a poison that killed them. Deadly Amanita mushrooms perhaps. There is a bean or seed found in holding rooms in central American pyramids which may have been feed to sacrifice victims that paralyzed them so that they did not thrash around while they were murdered. Could have been something like that.
(I thought hemlock, but it did not come to the Americas until the Europeans arrived. )
A grim subject. (Oh, Joseph Campbell would find something about it uplifting!)
Off to get some sunlight and fresh air!
:^)