Federal authorities are nearing the end of a three-year insider-trading probe that would dwarf any of its kind with its impact on the financial industry. One large focus of the investigation is the pervasiveness of so-called “expert networks” of independent analysts and consultants who try to glean nonpublic information from current and former managers of hundreds of companies to pass on to traders. Goldman Sachs has also come into the spotlight, as investigators examine potential leaks by the firm about mergers. The cases are being handled by federal prosecutors in New York, the FBI, and the SEC. Though they have not discussed them publicly, Manhattan U.S. Attorney Preet Bharara is known to have made uncovering insider-trading rings a top priority. "Illegal insider trading is rampant and may even be on the rise,” he said in October.