Jon Corzine plans to tell a House of Representatives committee that he doesn't know the location of clients' money that went missing from failed investment firm MF Global.

The former U.S. senator has been subpoenaed to explain how MF Global, which he led for about 20 months, collapsed into the eighth-largest bankruptcy in U.S. history and why an estimated $1.2 billion in client funds is unaccounted for.

In prepared testimony posted Thursday on the House Committee on Agriculture's website, Corzine apologizes to "all those affected" by MF Global's failure. The company filed for bankruptcy protection on Oct. 31. Corzine resigned as CEO on Nov. 3 and hasn't spoken publicly since.

"I simply do not know where the money is, or why the accounts have not been reconciled to date," Corzine says in the statement. He says he can't say whether there were "operational errors" at MF Global or whether banks or other companies have held onto funds that should be returned to MF Global.

Corzine, 64, said many people in his position would invoke their Fifth Amendment right to avoid answering questions _ a move that was widely expected. But he says that as a former senator he recognizes the importance of congressional oversight and will try his best to answer the panel's questions.

Corzine, however, leaves open the possibility that he will decline to answer some questions. He says that since his resignation from MF Global, he hasn't had access to certain information he might need to "reconstruct the events that occurred during the chaotic days and the last hours leading up to the bankruptcy filing."

"Without adequate time and materials to prepare, I may be unable to respond to various questions members might pose," he says.

Attempting to answer questions poses a risk for Corzine. Anything he might say could be used against him in a courtroom, should Corzine ever be charged in the case. The FBI and several federal regulators are investigating MF Global.

Lawmakers in both parties may have a lot to ask him. Some have heard from farmers, ranchers and small business owners in their districts who are missing money deposited with the firm.

Agricultural businesses use brokerage firms to help reduce their risks in an industry vulnerable to swings in oil, corn and other commodity prices. But MF Global increased risks by making big bets on European government debt _ bets that proved disastrous.

In his testimony, Corzine says MF Global sought to restructure the Europe investments in a way that reduced the risk to the firm. Corzine says he "strongly advocated" the investments and takes responsibility for them.

Legal experts say Corzine could be held personally liable for misrepresenting to investors the risks the firm had taken. Other top MF Global executives also could face legal jeopardy, they say. Corzine will say Thursday that the company's board signed off on the investments and was aware of the risks involved.

It's the first time in more than 100 years that Congress has subpoenaed a former senator to testify, according to Senate historian Don Ritchie. The occasion blends the two worlds Corzine has occupied for his professional life _ Wall Street and public office.

A Democrat, Corzine represented New Jersey in the Senate from 2001 through 2005. He later served as the state's governor. Before entering politics, he was CEO of Goldman Sachs from 1994 to 1999.

Several class-action lawsuits on behalf of shareholders have been filed against Corzine and three other top executives. A bankruptcy court is consolidating the suits. They accuse the firm and its leaders of making false statements about MF Global's strength and cash balances.

Corzine is expected to give the remarks starting at 9:30 a.m. Eastern time.

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Samantha Bomkamp contributed to this report from New York.