Archaeologists say wounds on a 430,000-year-old skull found in Spain would have been lethal, making it possibly one of the earliest cases of murder in human history.

Using modern forensic techniques, researchers have determined two blows to the head probably killed the victim before the body was thrown into a deep cave system in northern Spain.

The site in the Atapuerca Mountains is known as Sima de los Huesos, the "pit of the bones," containing bones fragments of the skeleton of at least 28 individuals.

Several Homo species have been found there, including Homo heidelbergensis and another species as yet unidentified that paleontologists simply call the "Sima de los Huesos hominin."

One skull, pieced together from more than 50 fragments, shows two holes above the left eye, the result of two impacts from the same object, researchers say.

The injuries are unlikely to have been the result of an accidental fall down the cave system's vertical entrance shaft, they add, since in such a case it would be extremely unlikely for the same object to hit the skull twice.

"The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict," says lead study author Nohemi Sala.

It is unknown what that object was, but it may have been a stone hand ax or a wooden spear, the researchers suggest.

"Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill," they say in their study published in PLOS One.

The sex and even the exact species of the individual has yet to be determined, the archaeologists say.

All of the remains found in the bone pit are too old to be members of our modern Homo sapiens species, they explain, leaving the possibility of the murder victim being an early Neanderthal or an even more ancient human ancestor.

As to why so many hominin remains were found in the cave system, the researchers suggest the site may have been used for disposal of deceased individuals.

Interpreting the site as a place where hominins deposited dead members of their social groups appears to be the most likely scenario to explain the presence of human bodies at the site, the researchers suggest.

If so, it could be an example of the earliest funerary behavior found so far in the fossil record, they say.