Airport spokesman Jan Van Der Cruijsse could not explain how the area could be so vulnerable. "We abide by the most stringent rules," he said, noting the same apply to other European airports.
Philip Baum, an aviation security consultant in Britain, called the robbery unsettling — not just because the fence was breached, but because the response did not appear to have been immediate. That, he said, raised questions of 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, raising the specter of terrorists exploiting such lapses as well.
Air transport is considered the safest way of transporting small, high-value items, logistics experts say, a fact reflected by relatively cheap insurance policies. Unlike a car or a truck, an airplane is unlikely to be waylaid by robbers once it is in motion. It's also considered highly secure before departure and after arrival because the aircraft is always within an airport.
The stolen parcels contained rough and polished stones bound for Switzerland, where many of the packages were intended for different handlers.
"What we are talking about is obviously a gigantic sum," De Wolf said, giving an estimate of $50 million.
A decade ago, Antwerp was hit by one of the biggest diamond heists in history. Robbers disabled an alarm system and took precious stones, jewels, gold and securities from 123 of the 160 high-security vaults at Antwerp's Diamond Center. The loot was so abundant the thieves had to leave some of it behind, police said, estimating the 2003 robbery to be worth about $100 million at the time.
Monday's heist was a fresh blow to Antwerp's major industry, which prides itself on discretion and security.
"This is causing quite some unrest," De Wolf said. "It was incredible how easily it all went. This is worrying in terms of competitiveness, since other diamond centers are ready to pounce and take over our position."
Juergen Baetz and Don Melvin contributed to this report from Brussels.