NEW YORK - The day after Bernard Madoff was thrown behind bars, investigators returned Friday to the arduous task of piecing together one of the largest frauds in history - and trying to determine if anyone else was involved.

The FBI has refused to discuss the status of an investigation expected to drag on for months. But experts say it's certain Madoff's closest relatives and associates are high on the list of people authorities suspect may have known about a scheme that was making them hundreds of millions of dollars.

“I think it's fair to say that his family is a subject of the investigation,” said George Jackson, a former federal prosecutor now in private practice in Chicago.

Madoff faces a maximum sentence of 150 years in prison after pleading guilty Thursday to 11 charges including fraud, perjury and money laundering, telling a judge he was “deeply sorry and ashamed.” The judge immediately jailed him - a decision his lawyers asked an appeals court to reverse on Friday.

Jackson predicted more indictments, potentially alleging a conspiracy by Madoff insiders. But he and others stressed the investigation still is in its early stages, and that Madoff's guilty plea had no bearing on its course.

Any potential suspects “are not better or worse off than they were before the plea,” said Christopher Clark, another former federal prosecutor in Manhattan. “The investigation is going to keep going along at its own pace.”

Given the enormity of the paper trail, Clark predicted it would be six months to a year before more charges are brought. Those studying Madoff's financial records have also said it is too early to know exactly where the money went over decades.

Court documents filed Friday show Madoff and his wife had a combined net worth of more than $823 million at the end of last year, including a $7 million yacht and four properties worth a total of $22 million. Last month, a court-appointed trustee overseeing the liquidation of Madoff's firm reported that about $1 billion in assets had been recovered from the business.

Part of the delay in any further indictments may be due to a lack of cooperation from key employees. David Sheehan, a lawyer for the trustee seeking to locate Madoff's assets, has complained that people with knowledge of the inner workings have “lawyered up” since Madoff's arrest late last year.

Among those under scrutiny are Madoff's wife, Ruth, who the Massachusetts securities regulation agency said withdrew $15.5 million from a Madoff-related brokerage firm in the weeks before her husband's Dec. 11 arrest, including a $10 million withdrawal on Dec. 10.

Mere references to Mrs. Madoff during her husband's guilty plea Thursday drew laughter from a mocking audience of investors still bristling over a disclosure several weeks ago that she wants to keep $69 million in assets, including the couple's $7 million Manhattan penthouse.

Mrs. Madoff faces potential civil litigation against her as a result of the collapse of her husband's financial empire. Her lawyer has declined comment.

Also on the radar are Madoff's brother, Peter, who was instrumental in making Madoff's investment firm a renowned operation. Madoff sons Andrew, 42, and Mark, 45, also worked for their father in a trading operation their father has insisted was “legitimate” and separate from his fraudulent investment advisory service.

In the days following his brother's arrest, Peter Madoff, 63, reported to work and helped regulators examine the company's books, his lawyer said at the time. He described his client as “100 percent cooperative.”

But the brother resigned about a week later and, like the rest of the family, has never spoken publicly about the case.

The sons, who worked closely with their 70-year-old father and shared his extravagant lifestyle, also have denied any wrongdoing through their attorney. The lawyer has called them victims of the scheme and claimed they had “no access to overall financial information about their father's firm.”

Besides the family, burned investors have questioned the role of Frank DiPascali, the chief financial officer of Madoff's money management business.

A lawyer for DiPascali declined comment on Friday. Attorneys representing the brother and sons did not immediately return telephone messages.

So far, federal authorities are believed to have spoken to several clerks who handled some of the voluminous paperwork Madoff admits he created to convince 4,800 investors that their nearly $65 billion in investments continued earning profits, even in bad years.

Madoff generated or had employees generate “tens of thousands of account statements and other documents through the U.S. Postal Service, operating a massive Ponzi scheme,” prosecutors said.

During his plea, the defendant claimed he started the scheme as a short-term way to weather the early-1990s recession - a timetable at odds with what authorities have alleged.

Assistant U.S. Attorney Marc Litt told the judge that the giant Ponzi scheme began “at least as early as the 1980s.”

Madoff also took all the blame for his fraud and tried to create a wall between himself and his family, saying his “other businesses” - proprietary trading and market making - were “legitimate, profitable and successful in all respects.”

He then added: “Those businesses were managed by my brother and two sons.”

Litt said the admissions were adequate for a plea but was quick to add that the government “does not entirely agree with all of the defendant's description of his conduct.”