Enforcement Directorate officials on Friday questioned former external affairs minister K Natwar Singh's son Jagat Singh in connection with the Iraqi oil pay-off scam.
Jagat had appeared before the ED on Thursday also, when a special team grilled him for over seven hours.
His interrogation came days after an ED team returned from a visit to Jordan and Iraq where they are believed to have collected details about bank transactions in 2001.
The directorate had summoned Jagat a few days ago for questioning in the wake of allegations by former ambassador to Croatia Aneil Mathrani that he was present in Baghdad at the same time as the official Congress delegation.
Jagat had admitted that he had accompanied his father to Iraq in January 2001.