A top MF Global Holdings Ltd. official says she expressed worry about the U.S. derivatives broker\'s risk of customer money four days before the firm collapsed. Christine Serwinski, the firm\'s former North American chief financial officer, became concerned after seeing a document showing \"a substantial deficit\" Wednesday, Oct. 26, 2011, in the amount of firm money used to protect customer accounts, Serwinski\'s prepared testimony for a congressional hearing Wednesday said. Other MF Global officials -- including Chairman and Chief Executive Officer Jon Corzine, who was previously a Goldman Sachs Group Inc. CEO and a Democratic U.S. senator and New Jersey governor -- testified last year they didn\'t know until late Oct. 30 the estimated $1.6 billion shortfall had developed until. Corzine denied knowledge of any improper transfers. Serwinski\'s discovery of the customer-funds deficit came a day after the firm reported a $191.6 million quarterly loss as a result of investing $6.3 billion in Spain, Italy, Portugal, Belgium and Ireland sovereign debt. The loss report scared off investors and led credit ratings agencies Moody\'s Investors Service and Fitch Ratings to cut their ratings on the firm to junk -- and Corzine quickly sought to find a buyer for the firm. \"To me, even though the regulations would allow it, I was not comfortable with the firm putting customer funds at risk, even just overnight, in that manner,\" Serwinski said in testimony posted online by the House Financial Services Committee oversight panel and reviewed by United Press International. She said in her testimony she asked how the deficit could have occurred and was told the \"firm had borrowed money\" from its futures unit, where some customer money was held, \"on an intraday basis and had missed the wire deadline to pay it back.\" Serwinski was on vacation at the time, but in checking in by e-mail and phone \"was assured that the matter was under control and being addressed and that the funds would be returned on Thursday [Oct. 27],\" she said in her testimony. On Saturday, Oct. 29, she was told customer money appeared to be missing, but was assured events were \"looking good\" and the firm was \"under control,\" she said in her testimony. Still a bit concerned but \"not alarmed,\" she cut her vacation short and returned to the office Sunday, Oct. 30. Before boarding her flight, she learned the firm was investigating an apparent shortfall in customer funds of as much as $600 million. \"At the time, I did not believe [such a large deficit] was possible,\" she said in her testimony. \"I thought that such a huge number could only be the result of an accounting error.\" When she got to the office, the North American controller and the regulatory controller told her \"there appeared to be a segregation and secured deficit of $900 million,\" which she still believed must have been an accounting error, she said in her testimony. But by the early morning hours of an all-night session to try to save MF Global, Serwinski was given a report by an assistant treasurer at the firm, Edith O\'Brien, that showed the customer deficit was real, Serwinski said in her testimony. Serwinski said she desperately sought to transfer funds to cover the customer-account shortfall in the final hours before the firm\'s collapse. \"I even requested my colleagues to ask the Federal Reserve to open its wire facility early on Monday morning [Oct. 31] to begin transfers, but we were unsuccessful,\" she said. \"Although we were able to move some funds into the [futures brokerage\'s] segregated and secured accounts, a number of submitted transfers were not executed by the banks, and we were unable to move sufficient funds to make up for the shortfall.\" MF Global filed for bankruptcy Oct. 31, the largest Wall Street firm to collapse since Lehman Brothers Holdings Inc.\'s $600 billion bankruptcy Sept. 15, 2008. Serwinski was to appear Wednesday with O\'Brien, General Counsel Laurie Ferber and Chief Financial Officer Henri Steenkamp. O\'Brien was expected to decline to answer questions, invoking her right against self incrimination, The Wall Street Journal reported.