Update: Further data changes this somewhat. See my post on 6/4/21 about the subject.The article from the Proceedings of the National Academy of Sciences combines standard archaeological techniques with newer genetic ones, which allows deeper understanding quickly. The genetic information shows that the fifteen individuals from a Polish site dating to 5000 years ago were not only related, but exactly how: a mother cradling a child, siblings buried side-by-side. The had been murdered, mostly by blows too the head. However, whoever buried them did not just throw them in a ditch, but placed them according to their relationships. They knew them well. Without the genetic identification of the victims, we would have only been able to guess at that part. Significantly, there are no older males among the fifteen. It is therefore likely that it was the older males who returned to find their four families executed, and buried them.
This was in the era when the Yamnaya, the Corded Ware people, the Indo-Europeans, were moving from the steppes into Central Europe. The previous occupants had an ancestry that was 15-30% Western Hunter Gatherer, and 70-85% Anatolian farmer, a group that had moved up a few thousand years earlier. They had no steppe ancestry. This group had no steppe ancestry either. They are in proximity to the Corded Ware people and in the right time period.
"Farmers" in this context likely meant cattle and sheep more than fields of grains. They would have grown some crops, and pig bones have been found nearby, which is always a sign of settlement. So they had both types of domesticated animal, those that had to be brought to new grazing territory, and those who had to be kept in one place. The most likely explanation is a raid, either by Indo-Europeans from the steppe, or by a more local group under pressure from the gradually encroaching Corded Ware people.