U.S. prosecutors may still be building a case against imprisoned swindler Bernard Madoff’s only surviving son, who according to sources was one of the “co-conspirators” mentioned in a plea deal by a Madoff associate last month. Two sources familiar with the Madoff case confirmed to Reuters that people identified only as “co-conspirators” in statements and court documents at accountant Paul Konigsberg’s June 24 plea hearing are Madoff’s sons, Mark and Andrew, who were employees of the Madoff investment firm.