The SEC kind of steps in as soon as they have reason to investigate, they even have a rather profitable whistleblower program (profitable for the whistleblower who gets between 10 and 30% of every fine above 1 million). The SEC is a civil agency charged with protecting "investors", not defrauded customers. The latter is, to the best of my knowledge, referred to prosecutors by the SEC (I think the southern district of New York).