According to reports, the interrogation took place at the official residence of the former Prime Minister. A team of senior CBI officials are said to have prepared to a questionnaire against which his replies were sought.
Rao was also asked abour the source of money and the alleged role of former Union ministers R K Dhawan, V C Shukla, Ajit Singh, Satish Sharma, former Haryana Chief Minister Bhajan Lal and industrialist Lalit Suri in the entire case. All of them have been named as accused in the case by the CBI.
The former Prime Minister is reported to have denied any role in the alleged payoffs. He is also said to have denied that he had any knowledge that Suraj Mandal, Simon Marandi, Shibu Soren and Shailendra Mahto had been paid money to vote against the no confidence motion on July 28, 1993.
The decision to question Rao is believed to have been taken at a meeting chaired by CBI director Joginder Singh on Tuesday.
CBI officials refused to confirm or deny that the former Prime Minister was questioned and said that the agency would inform the Delhi High Court, which is monitoring the progress of investigations, of the matter.
The CBI is supposed to present a comprehensive and final report on its findings before a division bench of the Delhi High Court on Spetember 9. Officials said that the findings have nearly made it certain that payoffs were made but it would be difficult to establish that former union ministers had a role in money changing hands.