DHAKA (Reuters) - Bangladesh police met an official of the U.S. Federal Bureau of Investigation (FBI) in Dhaka on Sunday to try to track down culprits in an attempted $951 million cyber heist from the country’s central bank.

Commuters pass by the front of the Bangladesh central bank building in Dhaka March 8, 2016. REUTERS/Ashikur Rahman

Initial investigations aim to identify the origin of a transfer order for $81 million that the Federal Reserve Bank of New York paid from Bangladesh Bank’s account there to casinos in the Philippines, a senior police official told reporters.

The transfer, one of the largest cyber heists in history, was among 35 requests that unknown hackers made for payments from the bank’s New York Fed account in early February.

Other requested transfers from that account, which Dhaka uses for international settlements, were apparently blocked.

Former finance secretary Fazle Kabir took over on Sunday as head of the central bank after the former governor Atiur Rehman resigned amid complaints from the government that it had only learned of the heist a month later from the media.

Also on Sunday, the wife of a cyber crime expert reported he had disappeared after being abducted from a motor rickshaw in the early hours of last Thursday. He had met police on Tuesday and told the media he knew three user IDs used for the heist.

Senior police official Mirza Abdullahel Baqui said after meeting the FBI official that criminals in six countries were apparently involved in the heist.

“This is the biggest transnational organized crime ever seen in Bangladesh and so we sought both technical and human assistance (from the FBI),” he said.

The officials also discussed how to proceed with their investigation, he added.

A government investigative committee led by former central bank governor Mohammad Farash Uddin began its probe into the heist on Sunday. “This is a wake-up call,” he said of the unprecedented breach in the bank’s computer security.

A Philippines Senate hearing last week was told that $30 million of the $81 million haul was delivered in cash to an ethnic Chinese casino junket operator in Manila. The rest was transferred to two casinos in the Philippines.

According to his wife, cyber crime expert Tanveer Hassan Zoha was blindfolded by unknown people in plainclothes early on Thursday before being taken away in a vehicle.

He had gone on Tuesday with a special police force to the central bank where they spent several hours. Afterwards, he told reporters he knew three of the user IDs involved in the heist.

Kamrun Nahar Chowdhury, Zoha’s wife, said police had refused to investigate her husband’s disappearance and she had appealed to the government for help to free him. Police were unavailable for comment.

“We don’t know why he was picked up,” she told Reuters.