Scientists have stumbled upon what may be the world's first known murder at an archeological site in Spain.

Examining fragments of a human skull found in the Sima de los Huesos (or "Pit of Bones"), also known as the SH site, the researchers writing Wednesday in the journal PLOS One described how they found evidence of blunt force trauma that may have caused the death of an individual some 430,000 years ago.

"This individual was killed in an act of lethal interpersonal violence, providing a window into an often invisible aspect of the social life of our human ancestors," Nohemi Sala, of the Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humano, told CBS News. "The site provides evidence of the earliest funerary practices found to date and suggests this behavior can be traced back to deep within the Middle Pleistocene time period."

The site, deep with in an underground cave system in northern Spain, is famous for its treasure trove of ancient remains.

So far, researchers have found 28 individuals that date back around 430,000 years and were hominin species belonging to the Neanderthal grouping. The only access to the site is through a 13-meter-deep vertical shaft, and researchers have yet to resolve how the bodies arrived there. They have been able to rule out carnivore activity or a geological event such as a sinkhole or landslide, leaving the possibility of accidental falls or intentional accumulation of bodies such as a burial site.

The evidence for the alleged murder revolved around 52 cranial fragments recovered during excavations at the site over the last 20 years. The skull shows two penetrating lesions on the frontal bone, above the left eye.

Relying on modern forensic techniques, such as contour and trajectory analysis of the traumas and a 3D imaging from a CT scan of the cranium, the authors showed that both fractures were likely produced by two separate impacts by the same object, with slightly different trajectories around the time of the individual's death.

A CT analysis of the Cranium 17 traumas. PLOS ONE

They said the injuries are unlikely to be the result of an accidental fall down the vertical shaft. Rather, the type of fracture, their location, and the fact that they appear to have been produced by two blows with the same object have convinced Sala and his team that this was a result of violence.

"Based on the similarities in shape and size of both the wounds, we believe they are the result of repeated blows with the same object and inflicted by another individual, perhaps in a face-to-face encounter," Sala said, adding the murder weapon could have been a wooden spear or stone hand axe.

The researchers acknowledge there have been other prehistoric murder mysteries - but those two individuals appear to have died in other ways.

In one of those cases, the Shanidar 3 Neanderthal shows a penetrating lesion to the left ninth rib, the researchers wrote, but it appears the individual "survived for several weeks after the lesion, and it is not clear that the final cause of death was related to the rib injury."

And the Upper Paleolithic Homo sapiens individual known as Sunghir 1 shows trauma to the first thoracic vertebra, which has been interpreted as the likely cause of death. "While this would seem to represent a relatively clear case of lethal interpersonal violence, the authors did not rule out the possibility of a hunting accident."

If the Spanish case proves to be the world's first murder, the researchers said it would demonstrate "that the lethal interpersonal violence is an ancient human behavior."

The latest findings are "completely compelling," said Debra L. Martin, Lincy Professor of Anthropology at the University of Nevada-Las Vegas and the co-editor of the International Journal of Osteoarchaeology, who did not take part in the study. The research shows this "social behavior that has been with us for a very long time."

"It is not particularly patterned or regularized in any sort of way when you look back into the Mesolithic or anywhere in the 'bloody' Neolithic," she told CBS News in an email interview. "It is nuanced, highly variable in it style, content, meaning and motivations, and I suspect the farther we push back and find straight up forensic evidence such as these authors have, we will find that violence is culturally mediated and has been with us as long as culture itself has been with us."

The researchers also said the finding "has important implications for the accumulation of bodies at the site."

"The only possible manner by which a deceased individual could have arrived at the SH site is if its cadaver were dropped down the shaft by other hominins," the authors wrote. "Thus, the interpretation of the SH site as a place where hominins deposited deceased members of their social groups seems to be the most likely scenario to explain the presence of human bodies at the site. This interpretation implies this was a social practice among this group of Middle Pleistocene hominins and may represent the earliest funerary behavior in the human fossil record."