Richard Bowen, a former Citigroup Inc. underwriter, had the ear of special investigators on April 7. Testifying before the Financial Crisis Inquiry Commission, Bowen said he had waited years to blow the whistle on Citigroup’s risky dabbling in mortgage markets.

Plaintiffs’ lawyers were listening, too. Two weeks later, Bowen’s testimony became the basis for a fresh filing in a securities lawsuit against Citigroup.