Could the $50 billion Bernard Madoff scandal turn out to have been a family affair?

Close relatives of Bernard L. Madoff who held senior positions at his investment firm all say they had no inkling anything was amiss until he stunned them in December by saying that Bernard L. Madoff Investment Securities was a Ponzi scheme.

Through lawyers or spokesmen, all have said they were shocked to learn of the scheme. Several of them, or their spouses, are said to have lost significant sums of their own money invested in the Madoff fund.

But as investigators piece together what happened, new information is raising doubts among lawyers involved in the case and experts on the operation of brokerage firms about whether the mammoth fraud could have continued for so long without the complicity or at least willful blind eye of one or more family members.

Focus is falling particularly on Peter Madoff, Bernard's brother and senior managing director at the firm, who as its registered chief compliance officer was responsible for ensuring that securities rules were followed and that regular tests were done to uncover fraud or other potential wrongdoing.

Steven Gomberg, a Chicago lawyer who specializes in financial industry regulation, said the compliance officer at Madoff's firm would have been obliged to check into where the trading was occurring, to learn why it was done outside the firm, and to confirm Bernard Madoff's public statement that the investment business was generating tens of millions of dollars in commissions.

New questions are also emerging about how the other close relatives could have been unaware of gross anomalies at the firm. All were bright, well educated, and familiar with the mechanics of securities trading and investing. Three of them had served on panels advising regulators on complex technical changes to securities rules.

To date, other than Bernard Madoff, no one at the firm has been charged with any wrongdoing. There is no word that any of the family members are under investigation. In addition to Peter, the close relatives there included Peter's daughter, Shana Madoff, a lawyer whose job was to give legal guidance on compliance with securities regulations, and Bernard's sons, Mark and Andrew, who together ran the firm's trading desk.

In particular, the recent discovery that billions of dollars worth of securities trades that Bernard Madoff claimed to have made for his investment fund never occurred is raising new questions about what family members knew or should have known, according to interviews with legal and regulatory experts involved in the case or familiar with it.