A grisly discovery deep in the Guatemalan jungle may cast new light on one of the ancient world's most beguiling mysteries - the collapse of the Mayan civilisation.
A grave containing some 50 bodies, buried in royal finery and bearing the marks of a vicious death, has been perplexing experts since it was unearthed earlier this year.
These are not the victims of "random violence", says Arthur A Demarest, the US archaeologist who has spent the best part of a decade fending off drug lords and looters as he excavated the 1,200-year-old site.
He says most of the dead, who include men, women and children, have been killed by "pulling the head back and shoving a large spear through the chest into the spine".
"You find war captives decapitated but not mass executions like this," he told the BBC News website.
Most remarkably for Dr Demarest, the attackers chose to abandon the site - the ancient trading city of Cancuen, grown rich through its position at the point where the river Pasion becomes navigable.
Winners in Maya warfare, he says, "normally conquered a place, put somebody on the throne. You would also put up some monuments bragging about what you had done."
Whoever conquered Cancuen, however, simply moved on.
A panel from Cancuen showing the king (pic: Andrew L Demarest)
As a result, the city abruptly lost its status as a key trading post along the Pasion, the river regarded as the lifeblood of the Mayas.
"This trade route dies and never comes back," Dr Demarest says, adding that Cancuen's collapse foreshadowed the decline of other cities along the river.
However, he warns, the sack of Cancuen should not be seen as a trigger of the Mayan civilisation's collapse.
Rather, says Dr Demarest, it can at best be treated as a "symptom" of the forces that finished off the Mayas.
Dr Demarest's findings, financed by the National Geographic magazine and by Vanderbilt University, were released last week and have yet to be scrutinised by his peers.
Many experts have cited geological evidence to argue that the Mayan civilisation died out after a famine caused by a crippling drought.
Massacres old and new
For Dr Demarest, the discovery caps a nine-year involvement with Cancuen, which began in the mid-90s after a peace accord ended Guatemala's civil war.
Many of the forensic experts enlisted to decode the secrets of Cancuen's ancient corpses had honed their skills investigating the relatively fresh massacre sites of the civil war.
Women at a funeral for bodies recovered from a civil war grave
Some 200,000 people died in 36 years of conflict between leftist guerrillas and Guatemala's US-backed military government.
Digging up the ancient grave, Dr Demarest says he was struck by how little human nature had changed over the centuries.
For his forensic team, the dig was a welcome distraction from the harrowing disinterment of the recently deceased.
"This is the first time they've worked on a massacre that took place earlier than 1980," he said.
"For them, it was a relief to dig this stuff up and not have widows crying around them."
He recalls how the discovery of a particularly well-preserved body prompted one of the team to exclaim: "Now we have evidence that can stand up in court!"
"There must be some kind of statute of limitations that applies to crimes committed 1,200 years ago," Dr Demarest responded.
'Too many suspects'
"We were not really expecting to find anything," says Dr Demarest, describing how the team stumbled upon the grave during a routine excavation of a pool at the base of a palace.
Dr Demarest has spent decades researching the Maya
He now expects the bodies to yield many clues about the way the Maya lived.
The corpses, he says, are remarkably well preserved, having been sealed for centuries in a muddy pool irrigated by the waters of a natural spring.
The precious jewellery buried respectfully with the corpses suggests they were "high nobles" but who killed them in this manner - and why - remains murky.
"It's a bit like an Agatha Christie mystery. There are simply too many suspects," says Dr Demarest, arguing that the most plausible of these is a tribe from the highlands, possibly tied to Cancuen by marriage.
Looters and bodyguards
Dr Demarest says there are plans to co-ordinate control of the site with the local Maya community.
With excavations in Cancuen set to continue, he hopes small groups of discerning tourists will begin visiting the region.
The attention the excavations have attracted from the Guatemalan media - and from the government - has already had a positive effect, he says.
The clandestine airstrips that had sprung up in the area after the civil war, serving as a transit point for Colombian drugs, have had to move elsewhere to avoid the publicity.
But Dr Demarest stresses he has had "no problems with anyone in the political landscape, only with the looters" - a gang of which he helped convict some years ago.
Now, he says, those looters are out for his blood. Watched over by freshly-hired bodyguards, Dr Demarest waits for the academic world's answer to his discovery.