In a scene worthy of George Clooney's screen alter-ego, the gentleman thief Danny Ocean, a robber threatens to blow up a high-end jewellery store on La Croisette in Cannes with a hand-grenade. While his accomplice points a gun at staff, the robber fills a sport holdall with expensive watches and heads for the door. Suddenly, he stops and turns. "Desolé," he says to the terrified sales staff, "C'est la crise." (Sorry, it's the economic crisis).

As a film script, the scene would have been cut as overly implausible. Of late, however, real life on the French Riviera has seemed even more unlikely.

Last Sunday, in a jewel heist described by police as "absolutely incredible" a lone thief strolled into a diamond exhibition at the luxury Carlton International, on the chic Croisette, and walked out 60 seconds later with $138m (£90.5m) in jewels.

Astonishingly, the robber fell as he jumped from a hotel window dropping his loot, but was still able to gather up the most expensive pieces and escape.

The daring daylight raid that resonated with Hitchcock's film, To Catch a Thief, entered the record books as France's biggest jewel theft.

Three days later, the apologetic thief targeted the Cannes jewel store, Kronometry.

Police are not linking the robberies – attributing the latter to nifty opportunists – but officers say the Carlton robbery bears certain hallmarks of the notorious Pink Panther gang suspected of carrying out two other high profile heists netting around $3 million in the French Riviera in the last two months.

The Côte d'Azur lives up to its double-edged reputation as a playground for the world's beau monde and what Somerset Maughan described as "a sunny place for shady people". Luxury yachts moored in the shimmering blue-green Mediterranean are more than a mirage of fantastic wealth.

When bored of bronzing, the rich go shopping. Often for diamonds. It is no secret that at the height of summer, the designer and jewel shops here are packed with valuable stock.

Interpol believes the Pink Panthers, named after the diamond in the Peter Sellers comedies, is a loosely affiliated gang of 200 jewel thieves from the former Yugoslavia.

Since the 1990s, the gang has been linked to dozens of spectacular robberies in 20 countries, including Dubai, Japan, London, Paris, Belgium and the United States, snatching jewels to the tune of some $500 million.

Their heists are characterised by impeccable planning, attention to detail, threats of extreme violence and Hollywood-style theatrics.

In Dubai, they drove a pair of limousines through a jewellery store window, in Paris, they donned blonde wigs and scarves to rob the Harry Winston store, in St Tropez they wore flowery T-shirts and escaped with their loot on a speed-boat.

Coincidentally, or perhaps not, a leading gang member was busted out of a Swiss jail just three days before the Carlton robbery. Milan Poparic, serving a sentence for a 2009 heist, was the third Panther to escape from jail in the last two month.

One "Panther", speaking to journalist David Samuels, who spent a year investigating the gang explained it emerged from the black market created by international sanctions against Serbia during the Balkan wars. It operates using a centralised command which picks targets and assigns crews to carry out jobs. The man told Samuels there were four main Panther groups originating from an original gang of diamond thieves from Montenegro.

The thieves in his group had travelled to Italy and seen how people lived there: "Some of us went insane and tried to have everything at once," he said. The greedy, rash ones wound up with long prison terms; others spent two or three years in Italian jails.

The most important, like Poparic, are sprung.

With impeccable timing, a new documentary about the Panthers is heading for British television. Smash and Grab is a gripping account of the Pink Panthers based on interviews with two alleged members who outlined its modus operandi. Among the films' claims is that gang members are addicted to beta-blockers to control their stress and paranoia.

In Cannes, the spate of jewel robberies has prompted angry calls by police unions for more armed officers on the streets as a deterrent. Frédéric Foncel, national secretary general of one of the main unions, claims promises to increase the police presence have not been kept and says town authorities refuse to meet union leaders, let alone listen to them.

"There are 200 police officers in Cannes; 60 of them are sitting behind desks instead of patrolling the streets," he said. "The authorities worry about delinquents and send the patrols out at night but all recent heists have been in broad daylight. It's staggering. There's no logic to it.

"What are the authorities waiting for ... serious violence or a death? It's a dangerous situation and it's damaging for Cannes, which is getting a reputation as an open window for criminals."

Whoever took them, the Carlton diamonds are unlikely to be found even if the thief is captured, says Vashi Dominguez, of the London-based Diamond Manufacturers.

"By now, they'll have been cut and polished, their shape and size changed without altering the value too much and nobody will be able to trace them back to the original gems," Dominguez explains.

"The thief could walk back into the Carlton wearing them and nobody would be able to prove they were stolen.

"I go to a lot of these exhibitions and I am always shocked by the lack of security in Europe especially given the value of diamonds and the fact that they are so portable."

In Smash and Grab, Chief Inspector Yan Glassey of the Swiss Central Brigade, who has long pursued the diamond thieves is interviewed in his office, where a large Pink Panther toy dangles from a noose.

"If you take all their crimes together, they are the best thieves in the world," Glassey says adding that hunting the gang is like a game of cat and mouse.

If the brazen robbery at the Carlton Cannes is the work of the Pink Panthers, however, it is clear that in this game the mouse has the upper hand.

• This article was amended on 5 August 2013 to remove a reference to schizophrenia which was inconsistent with the Guardian style guidelines.