Federal prosecutors and the FBI have been investigating possible illegal insider trading by two Securities and Exchange Commission enforcement attorneys who were in a position to receive sensitive information about agency probes of public companies.

The SEC's inspector general, David Kotz, found that the frequent stock trades over a two-year period by the pair raised suspicions of insider trading. Earlier this year, he referred the matter to the Fraud and Public Corruption Section of the U.S. attorney's office in Washington.

That office, together with the FBI, "is conducting an investigation of possible criminal and civil violations," Kotz told SEC Chairman Mary Schapiro in a memo dated March 3.

The memo and Kotz's report of his investigation were provided by the office of Sen. Charles Grassley, R-Iowa, who has been an active critic of the SEC's operations.

Kotz's report also found that the SEC "has essentially no compliance system in place to ensure that ... employees, with the tremendous amount of nonpublic information they have at their disposal, do not engage in insider trading themselves." The agency's disclosure and compliance requirements is based on the honor system and there is no way to determine whether an employee fails to report a transaction.