SEC inspector general H. David Kotz, seen left, started the probe in December after Madoff's massive Ponzi scheme came to light. Madoff is currently serving a 150-year prison sentence in a North Carolina medium-security facility.
For years, the SEC heard allegations of fraud but didn't take them seriously. Christopher Cox, who ran the agency at the time of Madoff's revelation, commissioned the investigation to figure out why.
Kotz didn't reveal the contents of the report, but told Fox Business that he would submit it to current SEC chairman Mary Schapiro Monday. The agency will determine when to make it public.
Back in January, Kotz told a congressional panel that his probe would be "independent and as hard-hitting as necessary" and vowed not to "hesitate to report the facts and conclusions as we find them."