Investigators looking into the disappearance of customer funds during the implosion of MF Global last month are coming to the conclusion that the money is likely gone for good, sources with direct knowledge of the matter tell the FOX Business Network.

What they don’t know is just how much money is missing.

That is likely to change as early as Friday, when bankruptcy trustee James Giddens provides an updated tally on the missing money, one of the focal points of civil and criminal investigations into the firm’s bankruptcy and a likely topic of conversation when the first of three Congressional hearings takes place this week.

The House Agriculture Committee on Thursday is scheduled to hear testimony from several witnesses, including MF Global’s former chief executive, Jon Corzine, regarding the brokerage’s demise. It was Corzine who changed MF Global’s business model from a plain-vanilla brokerage firm of commodities to a risk-taking outfit not unlike a hedge fund that ultimately led to its sudden downfall last month.

Read: Five questions lawmakers should grill Corzine on during testimony

Amid the firm’s implosion, as much as $1.2 billion of customer money remains missing; if executives of the firm purposely co-mingled customer cash with those used to run MF Global’s operations, that could lead to criminal fraud charges.

As of Monday, staffers for the House Agriculture Committee said Corzine’s attorneys had given no indication of whether Corzine will answer questions from the committee or remain silent by exercising his Fifth Amendment right against self-incrimination. Tamara Hinton, a spokeswoman for the Agriculture Committee, refused to comment on whether Corzine’s attorneys have given any further indication to the committee about his testimony, and a spokesman for Corzine declined comment.

One source close to Corzine said he has yet to make up his mind on the matter.  

Meanwhile, Giddens, the bankruptcy trustee for the brokerage firm, is preparing to meet a request from judge Martin Glenn, who is overseeing the case, on disclosing an update on the amount of money still missing. While the bankruptcy hearing won’t contain the same drama as Thursday’s Congressional hearing, for customers of MF Global its importance looms large.

Giddens has said as much as $1.2 billion is missing from customer accounts; other estimates are closer to $600 million still missing. So far, customers are expecting to recover about 65% of their funds.

One thing seems to be certain: Investigators and banks that have had extensive dealings with MF Global believe whatever money is missing is probably gone forever and won’t be able to be returned to investors when the investigation is complete, according to people with direct knowledge of the matter. That’s because even if customer funds are located, if they were used  to pay off legitimate claims of creditors those creditors are legally entitled to the money. (An MF Global spokesperson had no immediate comment.)

As a result, so-called claw-back provisions that cover ill-gotten gains, such as the customer money Bernie Madoff paid to his investors during his Ponzi scheme, do not apply.

In addition to the House Agriculture committee, the Senate Agriculture committee and the House Financial Services subcommittee on investigations will hold hearings next week on MF Global’s demise. Just today, the Senate Agriculture committee voted to subpoena Corzine to testify; the House investigations subcommittee is expected to do the same on Wednesday.

The action in Washington comes as a slew of securities regulators -- including the Commodity Futures Trading Commission as well as the US Attorney’s office for the Southern District of New York -- have launched investigations into MF Global's demise, focusing on whether executives made false statement about the firm’s financial health prior to its bankruptcy, as well as the circumstances behind the missing money.

MF Global, which long specialized as a broker of commodities for individuals and institutions, changed its business model with the 2010 appointment of Corzine, the former Governor of NJ, a U.S. Senator, and CEO of Goldman Sachs (GS). Corzine, a major financial backer of President Obama, vowed to transform MF Global into a mini-Goldman by placing bets in various markets around the world in an effort to ramp up profits.

But when news of his bets on troubled European sovereign debt was disclosed, investors began pulling money out of the firm and lenders yanked lines of credit, culminating in MF Global’s Nov. 1 bankruptcy filing.

But the bigger problem for Corzine and MF Global wasn’t the risk taking but how the firm managed its risk; investigators believe during the firm’s tumultuous final days that executives improperly co-mingled customer money with money used to run MF Global’s operations.

By law, customer money is supposed to remain separate, and according to people with direct knowledge of the investigation that money is probably gone for good, raising the stakes for Corzine as the investigations swirl.

It’s unclear how much detail about the missing money Corzine can, or will, provide during Thursday’s hearing, though people close to him are betting that in the end he will testify, but keep his testimony to the bare minimum.

“It’s just too embarrassing for a former U.S. Senator and someone close to the president to take the Fifth,” said one person who knows Corzine.

Charles Gasparino joined FOX Business Network (FBN) in February 2010 as Senior Correspondent.