Between 1997 and 2002, the team painstakingly excavated the remains of more than 40 decapitated and dismembered people who met their end some 7,500 years ago. Although the mound is one of earliest mass burial sites ever discovered, the archaeologists still aren't sure what they have on their hands.

Who dismantled the bodies and why? And were the teeth marks on the bones actually made — as they appear to be — by humans?

"We're trying to find out whether we're looking at warfare, cannibalism or some kind of ritual we don't know about," said Elizabeth Carter, lead archaeologist on the dig and a researcher with UCLA's Cotsen Institute of Archaeology. "We're just trying to piece together the evidence."