The Financial Crisis Inquiry Commission, that was created last year to examine the causes of the crisis in the nature of the 9/11 panel that examined intelligence failures preceding the terrorist attacks of Sept. 11, 2001, starts its first hearings with current and former executives of Citigroup to be probed there.

The commission will hear about the bank's role in spreading trillions of dollars in risky mortgage debt through the banking system. Besides, the panel will hear from former Federal Reserve Chairman Alan Greenspan; a former risk officer with failed subprime lender New Century Financial Corp.; and former executives and regulators from government-backed mortgage giant Fannie Mae.

During the three days the commission will be considering a firsthand accounting of decisions that inflated a mortgage bubble and triggered the financial crisis.

Citi was a major subprime lender through its subsidiary CitiFinancial. The bank pooled those loans and loans purchased from other mortgage companies and sold the income streams to investors. As borrowers defaulted, Citi absorbed losses on mortgage-related investments it held on and off its books.

Mortgage troubles at Citi, defunct investment bank Bear Stearns and elsewhere exposed cracks in the financial system. In late 2007 and throughout 2008, those fissures grew into a full-fledged credit crisis that crippled the global economy.