Sao 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 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.

Not a single shot was fired, she said, adding that while no one has been arrested, at least eight suspects have been identified. 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.

Police and reporters look at the tunnel Monday which highly sophisticated thieves spent three months digging under a busy city avenue to break into a Brazilian Central Bank in Fortaleza, Brazil. The crime, which netted 7 million was the biggest robbery ever in Brazil.

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 crawled in through a 28-inch-high tunnel that stretched 262 feet from a house they rented near the bank.

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.