The Financial Services Committee will question the SEC's internal watchdog Monday, as lawmakers try to learn why the regulatory agency failed to detect an alleged $50 billion investment fraud by Madoff.

Madoff's alleged Ponzi scheme will be a case study for a planned overhaul of laws regulating financial markets, said Rep. Paul Kanjorski, D-Pa., who will chair the hearing.

Witnesses include H. David Kotz, the SEC inspector general. He's already is looking into the agency's failure to uncover the fraud despite several warnings.

Kotz previously said he will examine the relationship between a former SEC attorney and Madoff's niece, who are now married.