Scientists have identified the murder weapon used to massacre 34 people in a German cave 5,000 years ago, as well as another person in Spain around the same time. To figure out how the ancient victims were slain, the researchers built and then smashed a series of fake skulls using popular Neolithic “weapon-tools”, noting the cranial trauma patterns produced by each type of bludgeon.

Explaining the logic behind their experimental walloping, the researchers describe how “an intensification of sporadic crisis within the European Neolithic societies” led to a marked increase in violent conflict. “In these contexts of interpersonal and intergroup violence, cranial injuries caused by stone axes and adzes are abundant,” they say.

Among the many examples of Stone Age bloodshed are the so-called Talheim massacre, evidenced by the 34 battered German skulls, and the pummeled cranium found at Cova Foradada in Spain. However, while it’s clear that all of the fallen were struck on the head with a blunt object, reconstructing the event and determining the exact murder weapon presents a major archaeological challenge.

To solve the mystery, the study authors created seven artificial skulls out of polyurethane covered with rubber skin. The fake noggins were filled with ballistic gelatin to represent the brain and then whacked with an axe and an adze – which is like an axe that has a blade perpendicular to the haft.

Wearing a white coat to prove that he’s a scientist rather than a madman with a Neolithic axe, 176-centimeter-tall (5’9”) study author Miguel Ángel Moreno-Ibáñez struck each skull from a different angle and at a different height, revealing the fracture patterns produced by the two tools.

“Although axes and adzes are very similar weapon-tools, there are a number of characteristics in the fracture patterns they cause that allow differentiation between the two,” write the researchers. For instance, “fractures caused by an axe are characterized by a symmetrical oval or drop-shaped fracture outline, with the point of impact located approximately at the center of the fracture.”

In contrast, “fractures resulting from adze strikes, in almost all cases, feature one straight (point of impact) and one convex side.” Experiments also revealed that striking a skull from a greater height increases the chances of penetrating through to the brain, suggesting that taller assailants may be capable of doing more damage.

Based on their reconstructions, the study authors conclude that the victims at both Talheim and Cova Foradada were probably killed with an adze. They were also able to determine that the latter was likely to have been struck from behind, indicating that the victim may have been executed rather than killed in a fight.

The study has been published in the Journal of Archaeological Science.