In his devastatingly persuasive 17-page letter to the S.E.C., Mr. Markopolos saw two possible scenarios. In the “Unlikely” scenario: Mr. Madoff, who acted as a broker as well as an investor, was “front-running” his brokerage customers. A customer might submit an order to Madoff Securities to buy shares in I.B.M. at a certain price, for example, and Madoff Securities instantly would buy I.B.M. shares for its own portfolio ahead of the customer order. If I.B.M.’s shares rose, Mr. Madoff kept them; if they fell he fobbed them off onto the poor customer.
In the “Highly Likely” scenario, wrote Mr. Markopolos, “Madoff Securities is the world’s largest Ponzi Scheme.” Which, as we now know, it was.