SÃO PAULO, Brazil — 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 robbery 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 São 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 São Paulo, was plundered over the weekend "by a group of highly sophisticated thieves," said Sabrina Albuquerque, a federal police spokeswoman.

Not a single shot was fired, she said, adding that while no one has been arrested, at least eight suspects have been identified. She said she did not know if more thieves were involved.

The Central Bank has begun its own 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 bank spokeswoman Beatriz Dornelles.

The heist took place sometime between 6 p.m. Friday, when the vault closes for the weekend, and 8 a.m. Monday when it reopens. The thieves broke into five containers filled with used Brazilian real notes worth about $22 million 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 destined to be burned.

List of major thefts, in order of amount taken:

1. $900 million in U.S. bills and as much as $100 million worth of euros — Iraq Central Bank, Iraq, March 2003. The thefts took place at the beginning of the U.S. invasion and were blamed on members of Saddam Hussein's family.

2. $67.8 million — Central Bank in Fortaleza, Brazil. Theft occurred sometime during weekend of Aug. 6-8, 2005.

3. $65 million — Knightsbridge Safe Deposit Center, London, July 12, 1987.

4. $50 million — Northern Bank, Belfast, Northern Ireland; Dec. 20, 2004. Widely blamed on the Irish Republican Army.

5. $37.5 million in gold — Brinks Mat Ltd., Heathrow Airport, London, Nov. 25, 1983.

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.

Police found a bolt cutter, a drill, an electric saw and a blowtorch, which were apparently used to cut through the vault's 3 ½-foot-thick steel-reinforced concrete floor, the police spokeswoman said. She said the thieves renovated the rental house and put up a sign indicating it was a landscaping company.