Thieves spent three months tunneling under a busy city boulevard in northeastern Brazil to break into a Central Bank vault and pull off the biggest burglary ever in South America's largest country.

The crime that netted $67.8 million was remarkably similar to a tunnel heist last year in which more than $1 million was stolen from a Sao Paulo company that transports money for banks. The suspected mastermind of that caper reportedly had escaped from prison three years earlier -- by digging a tunnel.

The vault in the city of Fortaleza, about 1,550 miles northeast of the capital, was plundered over the weekend "by a group of highly sophisticated thieves," said Sabrina Albuquerque, a federal police spokeswoman.

While no one has been arrested, at least eight suspects have been identified, Albuquerque said. She did not know if more thieves were involved. No shots were fired, she said.

The Central Bank began an internal investigation.

"We are looking into several aspects of the crime, including why the cameras and motion detectors inside the vault did not function and if the thieves had any inside help," said Beatriz Dornelles, a bank spokeswoman.

The heist took place between 6 p.m. Friday, when the vault closed for the weekend, and 8 a.m. Monday, when it reopened.

The thieves broke into five containers filled with used Brazilian currency notes worth about $22 each that had been collected from local banks for inspection by Central Bank auditors. Notes in good condition were to be returned to circulation, while worn notes were to be burned.

The thieves crawled in through a 28-inch-high tunnel that stretched 262 feet from a house they rented near the bank. Dug 13 feet below the vault floor, the tunnel -- which the robbers spent three months constructing -- had wooden panels and plastic sheeting lining the walls, as well as electric lighting.

Inside, police found a bolt cutter, a drill, an electric saw and a blowtorch, which were apparently used to cut through the vault's 31/2-foot-thick steel-reinforced concrete floor, the federal police spokeswoman said.

She said the thieves renovated the rental house and put up a sign indicating it was a landscaping company selling plants and natural and artificial grass.

"I never saw them selling anything, and, in fact, I never saw any plant or grass for sale in that house," said Richard Chamberlain, owner of a used bookstore next door.

"I'm not sure how many people worked in that house, but I would say more than five," he said by telephone. "The man who seemed to be the owner of the establishment was a friendly person who at times would pay for a round of beer in a nearby bar."

"He was a tall, balding and unshaven man who judging from his accent was from the south, maybe Sao Paulo," Chamberlain said. "He definitely was not from Ceara or anywhere from northeastern Brazil."

The bookstore owner said he never heard noises indicating tunneling or anything suspicious. "The tunnel was dug underneath one of the city's busiest and noisiest avenues, so it would be hard to notice anything unusual."

The biggest previous bank heist in Brazil took place in 1999, when thieves stole money worth about $16 million today from a Sao Paulo bank.

According to the Estado de Sao Paulo newspaper, police say the Fortaleza job and last year's similar robbery in the capital may have been masterminded by the same man -- convicted bank robber Moises Teixeira da Silva.

In 2001, da Silva was serving a 25-year sentence for robbery when he and more than 100 other inmates tunneled their way out of a prison in Sao Paulo.

In October of last year, at least eight men wearing monkey and clown masks broke through a bathroom of the money-transport company, Nordeste Transbank Seguranca e Transporte de Valores, after digging a 400-foot-long tunnel from a nearby house.

Wielding AK-47 semiautomatic rifles, the robbers forced about 75 workers tallying cash for automatic-teller machines to stuff the money in bags and fled back through the tunnel after spending only 10 minutes inside the building.

They made off with $1.6 million.

Federal police inspect the house where thieves began a tunnel to enter a branch of Brazil's central bank and steal $67.8 million from the vault.