RAB 1 Commanding Officer Lt Col Sarwar Bin Kashem said the online casinos were being operated through mobile phone software and application.
He made the statement while briefing the media on Tuesday after Monday's arrests of online casino kingpin Salim and three of his associates.
The mobile phone applications had instructions in Bangla, the RAB official said.
"If someone wanted to play P24 or T21, he had to install the application and open a free account. For payment, one had to use bKash, Nagad, Visa or Mastercard," he added.
If someone lost money, it would be deducted from his account. If someone won, money would be deposited into the account. That is how Salim had been running the online casino business, Lt Col Sarwar continued.
Members of Rapid Action Battalion (RAB) standing around the foreign liquor they recovered from casino kingpin Salim Prodhan's house in Gulshan 2, Dhaka on October 1, 2019 |CollectedOne of Salim's associates, Aktaruzzaman, fully operated the T21 game, the RAB official added.
RAB has learned that Salim and his associates had accounts for their online casino money with three banks, namely Jamuna, The City Bank and Commercial Bank of Ceylon PLC.
According to the investigation Tk9 crore had been transferred through these accounts, said the official.
RAB are searching if there is any other way the money changed hands, he added.
Later, Salim's associate Akhtaruzzaman would either cash out the money, or send it abroad.