The destroyed files comprise records of at least 9,000 preliminary inquiries into matters involving notorious individuals like Bernard L. Madoff, as well as several major Wall Street firms that later were the subject of scrutiny after the 2008 financial crisis, including Goldman Sachs, Lehman Brothers, Citigroup and Bank of America.
The S.E.C. is the very agency that is charged with making sure that Wall Street firms retain records of their own activities, and has brought numerous enforcement cases against firms for failing to do so.