Bernard Madoff's expected guilty plea on Thursday will probably bring at least partial answers to two of the biggest mysteries of his Ponzi fraud: How much money did investors really lose? And where did it go?

Madoff has waived indictment by a grand jury, and is due to plead guilty to as yet undisclosed charges that will be spelled out Thursday in a document known as a "criminal information."

Lawyers close to the case say they expect the federal prosecutors in Manhattan to make the document as detailed as possible, to make clear the scope of the wrongdoing they believe he committed.

While the fraud has been talked about almost universally as a "$50 billion" Ponzi scheme, it's clear that the amount investors lost is significantly less, at least in terms of the total amount they had actually invested.

Estimates, based almost entirely on speculation, have ranged from $10 billion to around $30 billion. Madoff himself purportedly told federal investigators that the fraud totaled $50 billion, but that evidently includes paper profits investors never actually earned; the cash they'd actually put into his fund is likely to have been much less.

At a recent Condé Nast Portfolio-sponsored panel on the Madoff fraud, former Securities and Exchange Commission Chairman Harvey Pitt estimated that the amount would come to around $17 billion.

The deadline for Madoff investors to file claims through bankruptcy court proceedings isn't until July 2, and Irving Picard, the court-appointed trustee overseeing the case, has said he expects thousands more claims to be filed by then.

So far, he hasn't disclosed any current tally of the amount of money allegedly lost by those who have filed claims already. Picard has said that the Madoff firm's books were in such disarray that he and his staff are still working to piece together information that may indicate how much really was lost.

The actual amount investors are out of pocket won't be known for some time. But the criminal information likely will contain a better-informed estimate, or some tally of the losses documented so far.

The trustee and prosecutors have been reviewing thousands of boxes of records found in the basement of the Manhattan office building where Madoff's firm was based, in a warehouse, and in a Madoff emergency backup facility located near LaGuardia Airport in New York.

The other big question is what happened to the money that was stolen during the fraud that lasted at least 13 years. Was it spent and is now gone? Or did Madoff hide large chunks of it, perhaps in secret overseas bank accounts?

There have been questions about the role his separate firm in London played, and as Condé Nast Portfolio reported last week, the Serious Fraud Office in Britain is looking into whether it may have been used to launder money from the fund.

But there are also indications that most of the missing money may have been spent, some on paying earlier investors who cashed out and some on the Madoff family's lavish lifestyle.

At the hearing Thursday, Madoff for the first time will face some of his angry investors; they are expected to be present for the guilty plea. And investigators are under intense pressure from anxious investors to answer these questions.