BRUSSELS – When the armored car set off for the Brussels airport carrying $50 million worth of precious stones from Antwerp’s diamond district, eight gunmen knew all about it.

One of the biggest diamond heists in recent memory was about to go down.

The thieves surely knew it would be too risky to make their move in Antwerp, which is the world capital of diamond-cutting, 27 miles from the airport. The city’s diamond industry has some 2,000 surveillance cameras, police monitoring and countless identity controls to protect its $200 million in daily trade of rough and polished gems.