Central Bureau of Investigation questioned the Income Tax officials, whose names were allegedly found in a register recovered from the residence of Chennai-based chartered accountant A Krishnamurthy, believed to be the main accused in the "cash-for-transfer" scam.

The CBI quizzed their role and "links" with the chartered accountant, who is alleged to have been "in the business of fixing appointments for Income Tax and Customs officials" for quite sometime, official sources said in New Delhi on Friday.

The sources said Krishnamurthy had also provided more leads into the case and the agency could quiz some finance ministry officials including those who had retired from the services.

The "cash-for-transfer" scam is believed to have been in operation for quite sometime now and thorough interrogations of senior finance ministry officials could only lead to the exact ramifications of the case, the sources said.

CBI was also searching for bank lockers of Krishnamurthy, though he claimed he had none. The CBI has already frozen his four bank accounts.

The scam came to light on May 22 after the personal secretary of former Minister of State for Finance Gingee Ramachandran, R Perumalswamy was arrested for taking bribe of Rs 400,000 from the residence of an Indian Revenue Service officer Anurag Vardhan, who has also been arrested by police.