How could this fraud have been prevented? Why is this a difficult fraud to prevent?

May 13, 1988, a Friday incidentally, will be remembered by a major Chicago bank. Embezzlers nearly escaped with $69 million! Arnand Moore, who was released after serving four years of his 11-year sentence for a $180,000 fraud, decided it was time to put his fingers in something a little bigger and better. He instigated a $68.7 million fraud plan. Naming himself as “Chairman,” he assembled Herschel Bailey, Otis Wilson, Neal Jackson, Leonard Strickland, and Ronald Carson to complete the formation of his “Board.” Most importantly, the “Board” was able to convince an employee of the Chicago bank to provide their “in.” The caper required one month of planning in a small hotel in Chicago and took all of 64 minutes to complete.
The bank employee had worked for the Chicago bank for eight years, and he was employed in the bank’s wire transfer section, which dispatches multimillion-dollar sums around the world via computers and phone lines. Some of the bank’s largest customers send funds from their accounts directly to creditors and suppliers. For electronic transfers, most banks require that a bank employee call back another executive at the customer’s offices to reconfirm the order, using various code numbers. All such calls are automatically taped. The crooked employee participated in these deposits and confirmations, and he had access to all the code numbers and names of appropriate executives with whom to communicate.