Image copyright AFP

It's a plot line that wouldn't be out of place in a Tintin comic - a French mayor, an Alpine climber, a historian, a wealthy Jewish stone merchant from London, and their tenuous connections to a bag of lost jewels discovered on the peak of Mont Blanc.

The trail begins early on 24 January 1966, as Air India Flight 101 starts its descent towards Geneva Airport. The pilot had miscalculated the aircraft's altitude and the Boeing 707 was heading directly for the summit of Mont Blanc, France's highest mountain.

All 117 people on board were killed as the plane crashed. "It made a huge crater in the mountain," a mountain guide who was first to reach the scene was quoted as saying. "Everything was completely pulverised. Nothing was identifiable except for a few letters and packets."

Various rescue attempts to recover bodies and debris were called off because of bad weather on the summit. Many remnants from the aircraft - including a bag of diplomatic mail and a wheel hub - have been gathered in the years since the tragedy, but pieces of twisted metal still lie in the peak's nooks and crannies.

Image copyright AFP Image caption The diplomatic mail bag discovered in 2012

Image copyright AFP Image caption A copy of the Hindustan Times Weekly, dated 1966 was discovered in 2008

It took half a century, however, for the crash site to reveal its biggest secret.

He was a mountaineer… and he didn't want to keep something that belonged to someone who'd died Sylvain Merly, Police Chief

Among the burning wreckage that was scattered across a glacier, a small case packed full of 100 precious emeralds, sapphires and rubies was flung through the air and swallowed into the ice.

The box, which two families are claiming had their name embossed into the side, sank into the glacier, only reappearing 47 years later clutched in the hands of a local climber as he strolled into the local gendarmerie.

The gendarmes heralded the climber's decision not to keep his find, with an estimated value of 246,000 euros (£205,000).

"You can see, he is very honest," said chief gendarme Sylvain Merly. "He was a mountaineer… and he didn't want to keep something that belonged to someone who'd died."

Merly took the jewels straight to the mayor of Chamonix, who stored them in a vault below the town hall until the media were told.

When the story came to light, journalists began to scramble for more details - at one point printing a photo of a mountain guide, Stephane Dan, with what appeared to be the jewels in front of him. In fact they were stones he snapped from gullies and sold for 20 euros each.

"It could have been me who found the real thing," he laments. "I climb all summer, collecting the best pieces of mineral to sell. I found many pieces of the aeroplane. I once found wheels. I found a special bottle used for coffee with Air India written on it. I even found the altimeter used for the plane."

Image copyright AFP Image caption Stephane Dan and a fellow mountaineer search for quartz on Mont Blanc

Bizarrely, this was the second Air India crash in the same area. Sixteen years earlier another plane, a Constellation known as the Malabar Princess, had gone down on the mountain, also on its approach to Geneva. So the wreckage of two aircraft is scattered over the area.

Dan said the local rumour was that the climber who discovered the bag of jewels was from Bourg-Saint Maurice, a village three hours' drive from Chamonix. "We all heard it was happening, but it was a mystery. Now we know it was a real - but even I don't know who it was."

It's so French, this story - you ask to see the stones and they send you a photo of them in a bag Francoise Rey, Historian

At this point, I started making attempts to film the jewels. But Sylvain Merly said he was no longer allowed to discuss the story with journalists, directing me to the prefect of the department of Haute-Savoie, in Annecy.

The prefect's office said they had nothing to do with the investigation and shunted me on to Francois Bouquin, head of the mayor's office in Chamonix. Bouquin said the Mayor's office was no longer responsible for leading the enquiry, pointing me to the court of Bonneville.

The court of Bonneville directed me to the court of Albertville, which, confused, sent me back to Bouquin - who said, in hindsight, he wasn't sure which courthouse was in charge.

After repeated calls and many hours spent on hold listening to Mozart's violin concertos, I pointed out to Bouquin that I had spoken to everyone he suggested. Then he finally gave an answer: "I don't want to have to tell you 'No'. But you cannot see the stones. At this time, it is a question of security. We are handling our own investigation into the case. We do not feel the media are useful or necessary at this time."

I was, however, able to persuade him to send me two pictures of what he called the "treasure", in the hands of the mayor, albeit wrapped in thick, white police tape.

"It's so French, this story," says Francoise Rey, a local historian and author of Crash au Mont Blanc, a book about the two Air India accidents. "You ask to see the stones and they send you a photo of them in a bag."

Image copyright Provided by the Mayor of Chamonix

An acquaintance of the mayor, Rey went to lunch with him and sat discussing a viewing of the treasure. But she, like so many others, drew a blank.

I am quite sure they are interested in keeping the stones and that they will do nothing whatsoever to help the families or the owner to prove they are theirs Francoise Rey

Rey is convinced that the mayor and the climber struck a 50-50 deal long before they told journalists about the jewels' existence. Under French law, there is a window of two years, she says.

"If no owner is found by then, one half will go to the Mayor of Chamonix and the other half goes to the climber.

"I am quite sure they are interested in keeping the stones and that they will do nothing whatsoever to help the families or the owner to prove they are theirs."

Fournier downplayed the allure of the jewels, she says, to dampen her interest. "He told me the stones are not so beautiful, and voila. They played the game that they were more embarrassed with them than happy, that's the impression they wanted to give."

Fournier, who is currently campaigning for local elections, was not available to answer questions, so Bouquin spoke on his behalf. "The suggestion we struck a deal is completely mad. There is no deal. We don't even know who found the stones. There is a law and a procedure that must be followed, and that is all."

Back in 1990, while Rey was researching her book, she was given access to a criminal dossier compiled by the local court of Bonneville, which contained many of the documents collated after the accident.

Looking through her notes, Mrs Rey made an amazing discovery. Annotated within the pages are the details of an insurance document making a claim for lost jewels destined for one man, who lived in London.

She had taken down the name of the family: Issacharoff.

Unfortunately, though, she failed to write down the claimant's initial. "I saw the letter. I don't have it, but I saw it. I have written in my notes the name of the person who was waiting for the stones in London. I am sure there are many more details in this letter. The main thing to do is to go back to find this letter. But this is proving very difficult."

Image copyright other

Since the dossier will not be opened to the public for 75 years, gaining access to the archive means a lengthy application process - one that Rey has only just began. How long it will take, she says, she doesn't know.

A quick internet search reveals the Issacharoff family to be one of the largest, oldest stone merchants in the UK. A family business started by the Russian-Jewish family in 1930, the Issacharoffs have become the largest coloured-stone importers in the country.

Avi, the current director of the business now called Henig Diamonds, says he can recall his father talking about the accident, and the family's collective relief that no relatives were on the plane when it hit the mountain. Normally when the family made a purchase of this size, one of them would go to pick it up in person, he says.

Grandson of Ruben and son of David, Avi is third in a line of directors of the business. His father can no longer recall the exact details. "We consulted our lawyers, but they told us we had no chance. We don't have records dating back 50 years. The only way we can prove the parcel was ours is that we know our name would have been written on the package."

The London-based Issacharoff family are not the only claimants to the jewels. Another set of Issacharoffs from Spain - no relation, but apparently also stone merchants - are reportedly approaching the French authorities in an attempt to gain access to the letter that Francoise Rey speaks about.

Bouquin, of the Mayor's office, says he has seen the packaging in which the stones were found, but it is not necessarily possible to make out a name from it.

"Maybe we might be able to identify the name on the parcel, but it is very hard to see. It has been 50 years beneath the ice."

Meanwhile, the days and months are ticking by.

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