The CBI has already filed a chargesheet in the case against Prasad, Rabri Devi and 14 others under charges of criminal conspiracy and provisions of the Prevention of Corruption Act, in which all the accused have been summoned on March 15.
According to the report, a fresh round of questioning is taking place as part of "further investigation" where the investigation agency is trying to ascertain the money trail and larger conspiracy.
Opposition launches sharp criticism
The fresh questioning of ailing Prasad, who was convicted in a fodder scam, and his wife had evoked sharp criticism from opposition parties on Monday.