She feared she would die during the ordeal, shouting, ‘Don’t kill me, I have babies.’

Baum-Gertner’s cause of death has not been released, but an investigating source said it was unexpected.

The source said: ‘Mr Baum-Gertner had been released on bail following his arrest over the Kim Kardashian robbery eight years ago, and was living in Paris, while regularly reporting to police.

‘His name was on the defendants’ list for the trial, and he was very enthusiastic about clearing his name in court.

‘This was until he died suddenly in the 10th arrondissement of Paris on March 6.’

The source continued: ‘He was suspected of liaising with mafia gangs from across the world over the Kardashian jewellery, and criminals are known to have issued threats against him following widespread publicity connected to the case.’

While Baum-Gertner refused to name any associates during multiple pre-trial interrogations, other criminals believed this might have changed when he was cross-examined in court.

There was the constant possibility that he would ‘name names’ as a means of keeping any possible prison sentence down, said the source.

Alleged ‘mafia’ buyers from Georgia, Israel, and the USA, are among those seen meeting up with Baum-Gertner in Antwerp, Belgium – the diamond capital of Europe.

All hoped to buy the Kardashian jewels and luxury watches, which were worth up to $10million in total, it is alleged.

Baum-Gertner had visited Antwerp at least eight times since October 3, 2016 – the day the gang broke into Ms Kardashian’s luxury apartment hotel during Paris Fashion Week and held her up using a vintage Mauser revolver.

Baum-Gertner was first arrested in January 2017, after regular meetings with Aomar ‘Old Omar’ Aït Khedache, the 68-year-old who has already confessed to being the ringleader of the Kardashian gang after his DNA was found at the scene of the crime.

The pair were caught on surveillance cameras at motorway service stations in the Paris suburbs, with Baum-Gertner arriving in his white Renault Scenic.

Rather than arrest the suspects straight away, officers from the elite Banditry Repression Brigade (BRB) of the Paris Judicial Police launched tailing operations.

Baum-Gertner’s numerous mobile phones were bugged, and a GPS tracking device placed on his car.

He was a well-known money launderer, counterfeiter, diamond dealer and ‘fence’ who always pledged to get the highest price possible for stolen goods.

Baum-Gertner regularly drove to Antwerp from Paris with ‘Old Omar’, as well as Christiane ‘Cathy’ Glotin, 78, and the only female defendant who will be in the dock on Monday.

A combined operation by Belgian and French detectives filmed Baum-Gertner and his associates meeting up with known underworld ‘faces’.

The prize asset stolen from Ms Kardashian was the easily recognisable 18.88 carat diamond and platinum engagement ring which American rapper Kanye West had bought for his future wife before their 2014 marriage.

The diamond was classified 11a – the purest type in the world because it has no measurable nitrogen or boron impurities – and signed LS, for Lorraine Schwartz, the New York designer loved by showbiz celebrities including Barbra Streisand, Beyoncé, and Angelina Jolie, as well as Ms Kardashian.

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The room in the Hotel de Pourtalès in Paris where Ms Kardashian was staying when the gang broke in

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Armed police standing guard outside the exclusive set of apartments in the French capital

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Chilling images (pictured) show the gaffer tape used to gag the star and bind her hands while the gang carried out the robbery

The LS made the tiny diamond very distinctive, and so particularly hard to ‘fence off’, according to enquiry sources.

Despite their reconnaissance, and obtaining search warrants to open dealer safes in Antwerp, police were never able to intercept the Kardashian swag.

Instead, during interviews following their arrest, the gang members said they were simply selling small amounts of melted gold.

Baum-Gertner himself told instructing judge Armelle Briand that he had also been buying gifts for family members in Antwerp, ‘but I never had the Kardashian jewels, and I never sold them.’

Rouen-born Baum-Gertner was brought up in a gypsy caravan for the first seven years of his life, before leaving school in the northern Paris suburbs aged 14.

Before his death, he had been convicted 11 times for receiving stolen goods and counterfeiting money, while also being linked with other jewellery heists, and other violent crimes.

In 2011, he was sentenced to four years in prison for the ‘aggravated theft’ of around $7million worth of Cartier diamonds.

They were taken from security vans by fake police officers using a car with flashing blue lights on A-roads close to Paris.

Throughout his trial, Baum-Gertner insisted, ‘I have no explanation to give, since I know nothing.’

All the while, Baum-Gertner tried to cover up his criminal activities with various legitimate ventures, including a lingerie retail outlet in the Paris suburbs.

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The robbers received a tip that a ‘big American star was coming to town’ and that she was showing off her fabulous wealth on Instagram. That tip allegedly came from from Florus Héroui (above), who ran a bar in Le Marais.

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Héroui is said to have got precise information about Ms Kardashian’s movements during Paris Fashion Week from Gary Madar (above), a VIP greeter who regularly met stars as they arrived at Paris Le Bourget airport by private jet

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Michael Madar, Bodyguard Pascal Duvier and Gary Madar are seen at Charles-de-Gaulle airport on September 29, 2016 in Paris

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Bodyguard Pascal Duvier, Gary Madar and Kourtney Kardashian are seen at Charles-de-Gaulle airport on September 29, 2016 in Paris

Marceau ‘Rough Nose’ Baumgertner (left) and Didier ‘Blue Eyes’ Dubreucq (right)

François ‘Big Guy’ Delaporte (left) and Pierre ‘Big Pierrot’ Bouianère (right)

He always tried to project himself as a regular businessman, despite having a pet dog named Al Capone, after the legendary American mobster.

Baum-Gertner’s last trial was in 2016, when prosecutors called for him to be imprisoned for his alleged role running the largest counterfeit banknote production workshop ever discovered in France, but a jury failed to convict him.

Detectives are meanwhile furious that the Kardashian trial has taken so long to get to court, saying that all those responsible for the raid could have been tried and potentially convicted as early as 2017.

In turn, the French authorities say court timetables have been clogged up by other big name trials, including of former President Nicolas Sarkozy, who has been found guilty and sentenced to prison on corruption charges.

There was also a fear that a Kim Kardashian trial would harm the five-star Paris tourist industry at a time of massive international events, including the 2024 Paris Olympics.

The Kardashian defendants originally numbered 12, but Pierre Bouianère, 72, and considered one of the ‘brains of the operation’ by prosecutors will also now be excluded.

The convicted drugs trafficker is suffering with Alzheimer’s, and his ill health means his alleged connection to the Kardashian gang will now be considered at a separate trial.

This means that a total of ten alleged gang members will appear in the dock on Monday, at a trial due to last until the end of May.

Aomar Aït Khedache and Yunnis Abbas, 72, have both confessed involvement in the robbery, while the rest deny any wrongdoing.

Michael Rhodes, Ms Kardashian’s US lawyer, said: ‘We can confirm that Ms. Kardashian will be testifying in person at the upcoming French criminal trial involving the 2016 incident in which she was bound and robbed at gunpoint by a number of masked assailants.’