ANTWERP, Belgium -- The thieves stood ankle-deep in a mess of diamonds, gold, jewelry, stocks, bonds, cash and lockboxes strewn on the vault room floor.

After outwitting security in the world's diamond-cutting capital and prying open 123 vaults, they had one unexpected problem: There was just too much loot to carry.

Two weeks later, authorities are still trying to figure out how much the thieves actually did get away with. Their rough estimate is $100 million.

That would easily make the Antwerp heist the largest safe-deposit box robbery ever -- twice the 1976 hit in Beirut, Lebanon, when a guerrilla group blasted its way into the vaults of the British Bank of the Middle East and into the Guinness Book of Records.

So far, authorities have three Italians and a Dutchwoman behind bars, but no clue where the loot is.

The suspected mastermind, 51-year-old Leonardo Notarbartolo, and his wife, Adriana Crudo, 48, appeared before a magistrate this week and denied any connection to the robbery. They were ordered held for another two weeks.

Investigators think the thieves started sizing up the formidable security challenges more than two years ago and beat the security simply by blending in.

Phantom company

Antwerp's director of judicial services, Eric Sack, said Notarbartolo, a dark-haired Italian who looks younger than his years, rented an office in the Diamond Center in 2000 under the name of a phantom company and slowly became part of the scenery. It did not matter that he had a criminal record in Italy. "He was not known here," said Nuyts.

Police are saying nothing about how the thieves got in, but in the week before the theft, investigators allege, Notarbartolo made several visits to the vaults, apparently to make sure the cameras could be disabled. His last visit was Friday, within the hour before closing time.

Then came the weekend of Feb. 15-16, when the guards at the Diamond Center were reduced to a single person, said Nuyts.

All eyes were on the nearby Sports Palace, where U.S. tennis star Venus Williams was winning the Diamond Games and coming within one victory of taking a $1 million diamond-encrusted trophy racket for good. At the same time, the thieves were scooping up that kind of loot every few minutes at the Diamond Center.

The thieves were undone, authorities claim, because of a sloppy cleanup. They threw bags with compromising material into a ditch alongside the highway and by chance police recovered them.