Around 6,200 years ago, a group of at least 41 men, women, and children were brutally murdered before being dumped in a mass grave in what is now eastern Croatia. Initially, the archaeologists who uncovered the grave in 2007 wondered if the victims were an entire inter-related community targeted for execution. But a new analysis reported in the journal PLOS ONE—including what is the largest genetic study of an ancient massacre to date—reveals that the victims were mostly unrelated. This surprising discovery raises more questions than it answers: Most significantly, why were these individuals killed, and who killed them? 

 “That’s the one million-dollar question,” says the study’s lead author Mario Novak, an archaeologist