It is the ultimate cold case file - a death 430,000 years ago that may be the first confirmed murder in human history.
Scientists used modern forensic techniques to determine the victim was probably killed by two blows to the head before being tossed down a cave system shaft.
The truth of what occurred at the Sima de los Huesos (Pit of Bones) site in the Atapuerca Mountains, northern Spain, was revealed after researchers pieced together 52 fragments of a near-complete skull.
They discovered two holes close together in the skull, above the left eye, caused by two separate impacts from the same object following slightly different trajectories.
The injuries were inflicted around the time of the individual's death and were not consistent with an accidental fall down the 13-metre deep vertical shaft.
Writing in the online journal Public Library of Science ONE, the Spanish and US-led international team concluded: "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.
"Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill."
The researchers, led by Dr Nohemi Sala, from the UCM-ISCIII Centre for the Evolution and Human Behaviour in Madrid, added: "This represents the earliest clear case of deliberate, lethal interpersonal aggression in the hominin fossil record, demonstrating that this is an ancient human behaviour."
The skull, known as Cranium 17, forms part of the skeletal remains of at least 28 individuals dating back around 430,000 years found in a chamber at the foot of the shaft.
Scientists believe they were deliberately deposited there after death. However, so far the only evidence of murder relates to the Cranium 17 skull.
The people whose remains fill the "bone pit" belonged to the genus Homo, the family of closely related species to which modern humans belong. But they are too old to have been part of our species, Homo sapiens. The Cranium 17 murder victim may have been an early Neanderthal, or a more ancient human ancestor, Homo heidelbergensis.
Only two other possible cases of murder exist in the fossil record, but the evidence relating to them is unclear.
One, a Neanderthal, died several weeks after suffering a penetrating wound to the body. However, it is uncertain whether the final cause of death was related to the injury.
The other, an early modern human from the Upper Palaeolithic period 10,000 to 50,000 years ago experienced a "sharp trauma" at about the time of death, but may have been killed in a hunting accident.