A suspect in one of the world's biggest bank robberies was arrested Friday after his sister-in-law tipped off police to his alleged involvement, authorities said.

Police said former security guard Deusimar Neves Queiroz (search) admitted a role in the $70 million theft in August from Brazil's central bank, providing thieves with information on the vault.

"A few years ago he worked for a security firm that provided services to the Central Bank," federal police spokeswoman Sabrina Albuquerque said.

So far, authorities have arrested nine suspects in the heist in Fortaleza (search), 1,500 miles northeast of Sao Paulo (search), and recovered more than $7 million of the loot. Thieves spent three months tunneling under a busy avenue to break into the vault.

Albuquerque said she didn't know why Queiroz's in-law, Francisca Rodrigues Cunha (search), turned him in. She added that the Cunha reported he was paid $890,000 for his role.

While the amount taken from the bank surpassed the $65 million stolen in 1987 from the Knightbridge Safe Deposit Center (search) in London, once recognized by experts as the planet's biggest robbery, it was dwarfed by the theft of $900 million in U.S. bills plus as much as $100 million worth of euros from the Iraq Central Bank in 2003.