SEC probes market professionals in flash crash
Schapiro said she was "deeply concerned" about the effects the volatile markets had on investors, in particular retail investors.
Two weeks after the Dow Jones industrial average dropped about 700 points within minutes, regulators are still trying to pinpoint the cause.
Schapiro reiterated the events of May 6 were unacceptable and her agency was taking necessary steps to implement safeguards.
(Reporting by Rachelle Younglai; Editing by Neil Stempleman)