Second, just 12 bodies? The Moche (of what is now Peru) were around at about the same time (100AD to 700AD or so) and make this look like a family picnic. They thought all those quite detailed scenes of sacrifice on their pottery were mythological until they found the graves of the people depicted on the pottery and some of the victims. Guess what happens when a culture has a god known to archaeologists as "The Decapitator" (picture a giant spider holding knives and heads). This article gives a pretty good summary of what they were up to.
Third, there is a bias in archaeology toward assuming that any culture is peaceful to the point of pacifism until proven otherwise. People like Lawrence Keeley and Steven LeBlanc have been working to debunk the myth of the peaceful savage. I highly recommend Keeley's book War Before Civilization on the subject. Simply put, there is plenty of evidence of ancient homicides out there, both murderous and as the rusult of warfare, that's frequently ignored by leftist academics who prefer their peaceful savage mythology.
You are correct about the Moche. Good point. El Brujo has depictions of some of their psychotic behavior.
You're probably thinking of the picture of the blood-drinking ceremony after the prisoners' throats were cut. I saw a display of Moche pottery at UCLA a few years ago, along with the amazing grave treasures of the "Lord of Sipan." The pottery was fascinating in many ways, including its skilled artisanship and lifelike representations of people and faces long dead.
The Moche, like most other South and Central American cultures, were in a constant state of war with neighboring city-states to find prisoners to sacrifice to appease their gods. A popular torture was skinning prisoners alive. One pot featured the agonized lipless face of such a sacrifice, its unprotected eyes staring pleadingly in a distillation of unbearable pain. Looking at it centuries after the fact was a powerful experience and I still wake up in cold sweats dreaming about it. Yet it was displayed along with playful pottery depictions of parrots, owls, sea lions, gourds and other subjects. Some of the pots were designed to whistle tunes as water was poured from them.