Mozkito / Photonews via Getty Images, file

The burned-out remains of the van used in the Feb. 18 diamond heist are shown in Zaventem, Belgium. Using a van and car to break down a security fence, a gang of robbers stole diamonds estimated to be worth $50 million from a plane bound for Zurich. Police have now arrested 31 people.

BRUSSELS - Authorities claimed a major breakthrough on Wednesday in their investigation of a spectacular $50 million diamond heist, detaining at least 31 people in a three-nation sweep some three months after robbers pulled off the theft with clockwork precision at Brussels Airport

A Frenchman who is believed to have been one of the actual robbers at the airport was arrested in France, while six to eight people were detained in Geneva, and 24 in and around Brussels. Police did not indicate what the other suspects' roles might have been.

What's more, police say they have proof that diamonds found in Switzerland were part of the cache that was spirited away in the brazen Feb. 18 robbery that ranks among the biggest diamond heists of recent times.

After two months of investigation on some of the suspects, police moved in. Suspects in France and Switzerland were detained on Tuesday, and the following day Belgian police carried out a massive operation, with 250 police involved in 40 house searches.

"In Switzerland, we have found diamonds that we can already say are coming from the heist, and in Belgium large amounts of money have been found. And the investigation is still ongoing," said Jean-Marc Meilleur, a spokesman for the Brussels prosecutor's office. He said police had also found luxury cars.

Meilleur was scant on detail, yielding no clues how police got on the trail of the suspects. Authorities were expected to announce later Wednesday how many of the detainees would be charged and arrested.

In Geneva, a police statement said that "a very important quantity of diamonds was seized" during the sweep "coming from the spectacular heist at Brussels airport." While Belgian authorities spoke of six detentions in Switzerland, Geneva police put it at eight, including a businessman and a lawyer. Authorities were alerted when suddenly a member of a major criminal organization appeared in their city. The value of the diamonds was still being estimated.

It was the first breakthrough in a robbery that many had started comparing to an "Ocean's Eleven"-type Hollywood script for its clinically clean execution during which no one was injured.

On a cold winter evening, the diamonds had been loaded on a plane bound for Zurich when robbers, dressed in dark police clothing and hoods, drove through a hole they had cut in the airport fence in two black cars with blue police lights flashing. They drove onto the tarmac, approached the plane, brandished machine guns, offloaded the diamonds, then made their getaway in an operation that barely took five minutes. Later that night, investigators found the charred remains of a van most likely used in the heist, but little else.

The stolen parcels contained both rough and polished stones. The trail ran dry until the surprise announcement on Wednesday.

Meilleur said that the man held in France is suspected to be one of the robbers. "This person has a very heavy judicial background in France and his extradition to Belgium has been requested."

Belgian authorities said that about 10 of the 24 people detained in Belgium were known criminals. The suspects ranged in age from 30 to 50, they said.

The diamond industry, too, was totally caught by surprise by Wednesday's developments. "But we can only be happy," said Caroline De Wolf, spokeswoman for the Antwerp World Diamond Center.

The Associated Press contributed to this report.

Related:

• Robbers snatch $50 million of diamonds off plane

This story was originally published on Wed May 8, 2013 6:40 AM EDT

Mozkito / Photonews via Getty Images

Firemen extinguish the burnt out remains of the van used in the heist near Brussels Airport on Feb. 18, 2013 in Zaventem, Belgium. Using a van and car to break down the security fence a gang of robbers stole diamonds estimated to be worth 50 million euros from a security van.

(Editor's note: An earlier version of this article led to a correction)

Eight armed and masked men made a hole in a security fence at the international airport in Brussels, Belgium, drove onto the tarmac and snatched millions of dollars' worth of diamonds from the hold of a Swiss-bound plane without firing a shot, authorities said Tuesday.

The gang used two vehicles in their daring raid Monday, dragged the cache of stones and sped off into the darkness, said Anja Bijnens, spokeswoman for the Brussels prosecutor's office.

Police found a burnt-out vehicle close to the airport later Monday night and said they were still looking for clues.

The heist was estimated at some $50 million in diamonds, said Caroline De Wolf of the Antwerp World Diamond Centre.

"What we are talking about is obviously a gigantic sum," De Wolf told VRT network.

An airport spokesman said the robbers made a hole in the perimeter fence and drove up to the Swiss passenger plane, which was ready to leave.

The robbers got out of the car, flashed their weapons and took the loot from the hold, said airport spokesman Jan Van Der Crujsse. Without firing a shot they drove off through the same hole in the fence, completing the spectacular theft within minutes, he said.

Van Der Crujsse could not explain how the area could be so vulnerable to theft. "We abide by the most stringent rules," he said.

The Swiss flight, bound for Zurich and operated by Helvetic Airways, was canceled. Swiss, an affiliate of Germany's Deutsche Lufthansa AG, declined to comment on the heist, citing the ongoing judicial investigation.

The insurance for air transport — handled sometimes by airlines themselves or external insurance companies — is usually relatively cheap because it's considered to be the safest way of transporting small high value items, logistics experts say.

Unlike a car or a truck, an airplane cannot be attacked by robbers once it's on its way, and it is considered to be very safe before the departure and after the plane's arrival because the aircraft is always within the confines of an airport — which are normally highly secured.

Philip Baum, an aviation security consultant in Britain, said the robbery was worrying — not because the fence was breached, but because the response did not appear to have been immediate. That, he said, raised questions as to whether alarms were ringing in the right places.

"It does seem very worrying that someone can actually have the time to drive two vehicles onto the airport, effect the robbery, and drive out without being intercepted," Baum said.

That amount of time would also allow someone to board the plane, he said.

A decade ago the Belgian city of Antwerp, the world capital of diamond-cutting, was the scene of what was probably one of the biggest diamond heists in history, when robbers took precious stones, jewels, gold and securities from the high-security vaults at Antwerp's Diamond Center, yielding loot that police in 2003 estimated to be worth about $100 million.

Antwerp's Diamond Center stands in the heart of the high-surveillance diamond district where police and dozens of cameras work around the clock, and security has been beefed up further since the spectacular 2003 robbery.

This story was originally published on Tue Feb 19, 2013 4:13 AM EST