When an amateur metal detectorist first heard his machine beep in an unpromising field in Lichfield in July 2009 and dug down to uncover gold, it was clear this was no ordinary archaeological discovery.

But who had collected the astonishing stash of gold, garnet weapons and ornaments he had found? Why had they been buried? And why were so many of them broken?

After a decade of conservation and analysis, archaeologists have finally revealed their conclusions about these tantalising questions and others, with the publication of the first major academic research into what became known as the Staffordshire hoard.

What they have concluded, according to Chris Fern, the lead academic on the project, reaffirms the hoard’s significance as “without a doubt one of the greatest finds of British archaeology” and casts new light on one of the most turbulent periods of early English history.

The archaeologists have even tentatively identified the Mercian king they believe may have once owned the booty, and can draw a tantalising link to the dynasty of the rival Anglo-Saxon ruler who was buried at Sutton Hoo, Britain’s most famous site of the period.

Dating from the period AD600-AD650, when the kingdoms of Anglo-Saxon England were battling for prominence, the Staffordshire find is in essence a “war hoard”, says Fern, consisting of spectacular items the experts believe were captured in battle by armies from the kingdom of Mercia, at the expense of neighbouring Northumbria and East Anglia.

The royal treasury was probably buried in haste at a time of turmoil, but for reasons that can only be guessed at, it was never reclaimed.

It includes items that are unique, such as a large processional cross that offers convincing evidence, say the experts, that Christian items were being carried into battle in this period as talismans.

A curious gold and garnet item, also without parallel and referred to for years as “the mystery object”, is now believed to have been a jewelled ornament that sat on top of a bishop’s headpiece. Both were deliberately bent and desecrated before being buried.

Of almost 700 items identified, about 80% are fittings from weapons, most of them from swords. But what is remarkable, according to the academics, is what they are made of. Gold sword pommels are extremely rare, though one was found at Sutton Hoo. The Staffordshire hoard contains 50. That finding alone completely transforms our understanding of Anglo-Saxon armies, according to Fern.

A reconstruction of a gold helmet from the period. Photograph: Birmingham Museums Trust

Rather than being limited to the ruler, gold weapons “must have been relatively commonplace for the warrior class beneath the king”, he says. “The poetry of Beowulf talks about huge gold treasure hoards and dragon hoards, but we always thought that was poetic license.

“What this hoard really shows us for the first time is a golden age in this period of Anglo-Saxon England – and I mean that literally. This was a period when gold was suddenly much more available, and was converted into beautiful objects for the warrior elite.”

Much of the past decade has been spent making sense of thousands of tiny gold fragments – about 4,600 – which Fern describes as “a case of multiple jigsaw puzzles being tipped together, mixed up and some of the parts being removed”. Some years into the project, the experts realised they had pieces of a rare gold helmet, two replicas of which are housed in museums in Birmingham and Stoke-on-Trent, which jointly own the hoard.

But what of the hoard’s original owner? Certainly, there are clues. The treasure was buried in Mercia, what was to become the royal heartland of that kingdom, at a time when it was notching up significant martial victories over its neighbours.

All of which may point in the direction of King Penda, who ruled Mercia for three decades until his death in AD655. Among the rivals he defeated and killed were the East Anglian kings Sigeberht and Anna, who were the stepson and nephew respectively of Raedwald, the East Anglian monarch who is believed to be buried at Sutton Hoo.

“There’s nothing in the hoard that is stamped Penda Rex, sadly, so we can’t say for certain that it is Penda’s hoard,” says Fern, but it is “very plausible”, he adds with academic understatement, that the collection includes booty Penda seized from Raedwald’s immediate successors.

For all the academics’ conclusions and occasionally “bold interpretations”, he stresses, the answers to many of the hoard’s questions will never be conclusively proven – “just as it is impossible with any great archaeological mystery to come up with an answer, unless you have a time machine. But that is part of the wonder of the hoard.”