Minnesota’s largest financial fraud continues to contain numbers that confound.

The latest eye-popping figure is $24 billion, as in a $24 billion lawsuit filed accusing then-M&I Bank of complicity in the $3.65 billion Ponzi scheme that operated under the watch of former Wayzata businessman Tom Petters.

Filed by a bankruptcy trustee in Florida, the suit asserts that M&I, which was acquired by BMO Harris Bank in 2011, knew of the Petters fraud yet allowed millions and millions of dollars to routinely flow through bank accounts assigned to Petters Co. Inc. (PCI), the corporate conduit for the scheme.

M&I served as “a critical linchpin” for the Petters operation by “legitimizing” and “facilitating” the decadelong operation, according to the lawsuit.

“M&I had actual knowledge of Petters’ fraud and provided substantial assistance, helping it flourish,” the suit said.

Through spokesman Patrick O’Herlihy, BMO Harris said, “There is no merit to these claims, and we will defend ourselves vigorously.”

Barry Mukamal, the Florida trustee, is attempting to recover money on behalf of two Florida hedge funds that invested heavily with Petters and suffered substantial losses when the Ponzi scheme was exposed and imploded in September 2008.

The Minnesota trustee in the Petters corporate bankruptcy has also sued BMO Harris over M&I’s relationship with PCI and the Petters operation. That case, which was filed nearly two years ago, seeks at least $68 million in damages.

The Minnesota lawsuit says, “Without the substantial assistance that M&I provided, the Ponzi scheme would have been discovered earlier by law enforcement authorities and victims of the Ponzi scheme.”

“We are awaiting trial,” said Doug Kelley, trustee in the Minnesota bankruptcy. “I’m looking forward to listening to a BMO Harris attorney explain to a Minnesota jury how nearly $40 billion can pass through a PCI account without making a special inquiry and without notifying federal regulators.”

The new case, filed in U.S. Bankruptcy Court in Florida, asserts that a small M&I branch in Edina was the banking home for the Ponzi scheme and that over the course of nine years, PCI deposited more than $37 billion in tainted funds in an account there and transferred out “virtually all” of those funds.

“M&I had actual knowledge that despite the astronomical incoming and outgoing activity, the average daily balance in the PCI account rarely exceeded a few million dollars. This reflected massive money laundering,” the suit says.

The suit said the large flow of money even attracted the attention of M&I’s money laundering department but the bank did nothing.

The Ponzi scheme centered on ruse to investors that their funds were being used by PCI to purchase consumer electronic goods at the wholesale level from manufacturers for resale to big box retailers such as Costco, Wal-Mart and Best Buy. But there were no goods and no payments from retailers as promised. Instead, money from new investors was used to pay off older investors and finance the acquisition of companies such as Sun Country Airlines, Polaroid and Fingerhut, the catalog retailer.

According to Mukamal’s lawsuit, M&I was fully aware that there were no deposits from retailers in the PCI account.

“This directly contradicted what M&I knew PCI had represented both to M&I and to PCI’s lenders,” the suit says, adding that M&I took no action “because of its desire to profit from and bolster its relationship with Petters.”

The lawsuit also alleges that M&I destroyed electronic and paper e-mail correspondence regarding its PCI relationship before 2005.

The Florida trustee is seeking to recover $24 billion that investors, including his two hedge funds, sent to phony suppliers set up by the Petters operation. The suit claims that M&I participated in the fraudulent transfer of money.