(Reuters) - U.S. futures industry investigators are looking into why Iowa-based collapsed brokerage PFGBest used a tiny accounting firm that appears to be operating from inside a suburban Chicago home to audit its books, according to a person familiar with the matter.

Experts said the use of such an auditor should have been a red flag to regulators of a futures brokerage with more than $500 million in assets and several hundred employees across the United States as well as in Shanghai and Canada.

There are comparisons with the way convicted Ponzi schemer Bernard Madoff used an auditor operating out of a strip mall in suburban New York and convicted swindler Allen Stanford's investment firm retained a little-known auditor on the Caribbean island of Antigua.

PFGBest's financial statement ended December 31, 2010, shows that a firm called Veraja-Snelling Company, based in Glendale Heights, Illinois, certified that the futures broker was in compliance with federal commodities regulations governing the segregation of customer money.