The tough week for Goldman is about to get tougher. After a full day on Capitol Hill testifying before lawmakers on the subprime-mortgage crisis and the SEC's recent civil suit against the company, Goldman and its execs are reportedly now under criminal investigation. Charges haven't been filed, but the probe comes at a time when the public is calling for more accountability on Wall Street and as a bill for financial regulation is working its way through Congress. However, the government has its work cut out for it if it decides to prosecute: Just last year, prosecutors lost a high-profile fraud case against two former Bear Stearns executives. With Goldman, the government will have to show the firm or its employees were aware of committing fraud in their mortgage business.