The FBI is investigating four major U.S. firms whose woes helped lead the country to the doorstep of a historic bailout plan put forth by the Bush administration last week, and debated in living rooms across the U.S. this week. The Wall Street Journal broke the story Tuesday evening that officials were looking into the possibility of fraud at Fannie Mae (FNM), Freddie Mac (FRE), Lehman Brothers Holdings Inc. (LEH) and insurer American International Group Inc. (AIG). Spokespeople for all four companies have thus far declined to comment to the press. The fraud probes come as legislators are grappling with what has been dubbed by many as "the mother of all bailouts," a proposal by administration officials that would cost anywhere from $700 billion to $3 trillion, depending on whose estimates you believe. The four new firms under investigation bring the FBI's mortgage-fraud investigation case load to 26 firms and 1,400 distinct cases, the Journal reported. At issue with all four troubled companies is whether they misrepresented their assets, according to various published reports. All four were large players in various sides of the U.S. mortgage market. The government seized control of both Fannie and Freddie two weeks ago; the plan put in place then could require the Treasury to spend as much as $100 billion for each, if needed to backstop their ongoing operations, which are seen as critical to both the mortgage and broader financial markets. Last week, the Federal Reserve provided an emergency $85 billion loan to AIG, which faced bankruptcy largely over concerns that the insurance giant had unmanageable exposure to mortgage-backed securities and related investments. Lehman Brothers, for its part, headed into bankruptcy last Monday after federal regulators declined to bail the company out; Lehman was one of the largest Wall Street investment banks in the mortgage space. Disclosure: The author held no relevant positions when this story was published. Indirect holdings may exist via mutual fund investments. HW reporters and writers follow a strict disclosure policy, the first in the mortgage trade.