An investigation in the United States has found the Securities and Exchange Commission failed to uncover a $US96.6 billion fraud carried out by financier Bernard Madoff over a 16-year period.
The SEC inspector general says this happened despite many complaints and five separate investigations into Madoff's business dealings.
However, the report found no evidence of improper ties between the agency and Madoff.
Madoff, 71, was jailed for 150 years at the end of June. He admitted defrauding thousands of investors through a Ponzi scheme which he said had been running since the early 1990s.
The BBC reports a congressional hearing in February severely criticised five high-ranking SEC officials for their failure to stop Madoff earlier - three of them have now left the agency.
Madoff's firm was investigated because it made exceptional returns, but no irregularities were officially reported.
Madoff's demise was prompted by the global recession. Investors tried to withdraw about $US7 billion from his funds and he could not find the money to cover it.
New SEC chair Mary Schapiro has promised reforms, saying the agency taken steps to better detect fraud when it occurs.