April 6, 2013
DUCA didn't need to read the discussions.
If lots of people were adding $10,000, $20,000, or $30,000 to their 2.5% promo account through the backdoor after the account was closed to more funds in May, then there would be a significant increase in the balances and consequently the interest DUCA was paying on those accounts.
DUCA would have suspected something was up when the interest paid each month exceeded what was budgeted and was climbing faster than expected 2.5% / 12 = 0.2083% per month from the compounding of interest.
DUCA likely thought it was an interest calculation error or a rogue employee was continuing to move funds into those accounts after the promotion end date. They investigated further and discovered the cause was neither.