Mass grave in Croatia contains 41 individuals killed 6200 years ago in single indiscriminate event. DNA analysis shows 70% lacked close kin among victims, indicating subset of larger local population. Equal males and females killed, ruling out inter-male battle or sex-targeted reprisal. Cranial injuries on 13 victims indicate systematic violence or executions. No evidence of migrant conflict, family targeting, or ritual murder. Victims from early pastoralist community, predating known large settlements. Climate change disrupted resources like water, vegetation, and game, spurring territorial conflicts. Population growth overextended local resources, fueling expansion and violence. Multiple radiocarbon dates confirm single burial event. Most deaths likely violent despite lacking skeletal trauma evidence from soft-tissue injuries. Oldest documented indiscriminate mass killing challenges views of peaceful early agriculturalists.