The comments by Mohammad Shah Alam of Criminal Investigation Department are the first sign that investigators have got a firm lead in one of the world's biggest cyber heists.
He said arrests are likely to take place very soon.
On Thursday, the head of a Bangladesh government panel that investigated the heist said five bank officials were guilty of negligence but that they were only unwitting accomplices.
Shah Alam told Reuters his investigations had discovered that some bank officials had knowingly created vulnerabilities in the bank's connection to the Swift system, used for global transactions.
"Bangladesh Bank's Swift network was made insecure by some bank employees in connivance with some foreign people," he said. "They knew what they were doing."
He said investigators were now trying to find out how the mid-ranking officials were connected to the hackers and whether they benefited financially from the heist. Asked if the officials would be arrested, Shah Alam said: "We are very close to it."
Bangladesh Bank spokesman Subhankar Saha declined to comment.
Another investigator, who declined to be named, said more than 100 Bangladesh Bank employees had been interviewed in connection with the heist, and some were barred from leaving the country.
The hackers used fake orders to order the transfer of nearly $1billion from Bangladesh Bank's account at the New York Fed, using the international Swift payments network.
Many of the transfer orders were blocked or reversed but $81million was successfully transferred to four fake accounts in a branch of Rizal Commercial Banking Corp (RCBC) in the Philippines. Most of the funds then disappeared into Manila's loosely regulated casino industry.