BUENOS AIRES, Feb. 12 -- The hostage standoff was stretching into its seventh hour, with hundreds of police officers surrounding the bank. After negotiating a peculiar swap -- four hostages for some pizzas and sodas -- the captors inside seemed suspiciously quiet. So police stormed the building.

They found the 19 remaining hostages safe and sound, but the captors had vanished. A hole in the basement wall was covered with an iron lid that had been bolted shut from the other side. Later, police discovered that the hole led to a secret tunnel, which hooked into a municipal drainage system that emptied into the La Plata River. It was a clean getaway.

"Until now, in the history of Argentina there has never been a band of thieves that's had the audacity, the logistics, the preparation and the luck that this group of criminals had," a Buenos Aires provincial police investigator, Osvaldo Seisdedos, told reporters after the heist three weeks ago.

But those bandits have had some stiff competition. In the past six months, tunneling bank robbers in South America have broken world records of crime, snatching millions of dollars from banks and making their getaways through narrow passages beneath busy city streets.

The subterranean thieves in Argentina last month got away with cash and safe-deposit box contents worth an estimated $25 million to $70 million, according to police and lawyers representing bank customers. If those estimates are accurate, the robbery would be among the biggest bank heists in history -- a list currently topped by a $68 million job pulled off five months earlier in Fortaleza, Brazil. There, thieves dug a 260-foot tunnel from a house to the bank, equipping the passage with electric lights and wood-paneled walls.

News reports of the Argentine caper suggest almost everything went as the thieves had planned: The hostages were allowed to talk to relatives on cell phones, and the robbers even sang "Happy Birthday" to one of them. What the thieves really wanted, it seemed, was time to get more than 140 safe-deposit boxes loaded into the tunnel.

"Everyone I know is talking about it and saying the same thing -- that the people who did it are geniuses," said Salvador Peluso, 37, who works at a water-sports store across the street from the bank. "They robbed a bank without a single gunshot being fired and got away with everything. It's like a good movie."

Or a horror movie, to those who lost safe-deposit boxes. Many Argentines avoid bank accounts because of the financial sector's tumultuous recent history. Before the nation's economy collapsed in 2001, the value of the Argentine peso equaled the U.S. dollar's. Those who had deposited their dollars in savings accounts watched their fortunes largely disappear overnight -- the banks converted the money to pesos at the time of the collapse, and the pesos immediately lost most of their value. Throughout the country, many people vowed never to put another cent in a bank account.

In last month's crime, bank cash accounted for about $200,000 of the millions stolen, according to bank officials; the vast majority of the plunder came from the privately held boxes.

"Safe-deposit boxes seem to be an Argentine habit because people understand that banks are very insecure here," said Nydia Zingman, an attorney representing dozens of the robbery victims. "But the bank is ultimately responsible."

Similar robberies have allowed Zingman to carve out a legal niche for herself in Argentina; she has represented hundreds of clients who have lost safe-deposit boxes to tunneling robbers since 1988, she said. In 1997, she helped some of the owners of 370 boxes stolen at a bank to obtain compensation for lost money and valuables. After that robbery, neighbors told police they had heard digging sounds underground for months, and police found a tunnel stretching from the bank to an office building across the street.

Perhaps the most audacious tunneling robbery was the one last August in Fortaleza, Brazil. About 100 yards from Fortaleza's Central Bank, a sign appeared in front of a house that described it as a landscaping store -- a ploy, apparently, to defuse suspicions when the building's tenants removed large quantities of dirt from the premises.

The robbers entered the bank when it was closed for the weekend and got away with about $68 million. Previously, the largest bank robbery was one at the Knightsbridge Safe Deposit Center in London in 1987. The largest known bank-related crime in history is the embezzlement of nearly $1 billion from Iraq's Central Bank in 2003 by members of President Saddam Hussein's soon-to-be-deposed government.

In the months since the Fortaleza robbery, police have recovered about $8 million and arrested eight people they suspect were part of a large gang of thieves responsible for the crime. The massive amount of money yet to be recovered has led to kidnappings of alleged suspects for ransom.

In October, one of the men widely thought to have helped plan the robbery was kidnapped, then found dead after his family reportedly paid $890,000 in ransom. Two policemen have been arrested in connection with that crime. On Thursday, kidnappers released the sister-in-law of another suspect after failing to collect a ransom.

Argentine authorities would not discuss their ongoing investigation for this article, but they have told Argentine newspapers that they think some of the people responsible for the Fortaleza robbery were involved in the Buenos Aires heist. They also suspect that some members of the gang might be connected to other tunneling bank robberies in Uruguay and the Argentine city of Cordoba.

"However long it takes, the criminals will be arrested and will have a sweet anecdote to tell their prison cellmates," Argentine investigator Seisdedos told reporters at a news conference days after the crime.

According to Brazilian press reports, one potential suspect sought by authorities is Moises Teixeira da Silva, who was sentenced to 25 years in prison for organizing bank robberies using tunnels.

He escaped from a Sao Paulo prison in 2001 -- through a tunnel.