Sandip Ghosh, the former principal of RG Kar Medical College and Hospital who is in CBI custody, was questioned on Wednesday about how he had come to know the three men arrested with him on charges of financial irregularities, sources in the agency said.

He was quizzed about how bio-medical waste of the medical college was disposed of, the procedures followed in disposing of the waste and the personnel involved in the sale of the waste, the sources said.

The officers who questioned him wanted to know about certain financial transactions in which the three men — Afsar Ali, Biplab Singha and Suman Hazra — were allegedly involved.

The transactions, the sources said, were under several heads, including recycling of bio-medical waste.

On Tuesday, the CBI said Ghosh and the other three were part of a “great nexus” involved in “illegal financial transactions” at RG Kar.

CBI lawyer Ram Babu Kanojia said during his submission at the special CBI court that the nexus involving Ghosh and the other three was involved in granting favours for money at the medical college.

Sources said Ghosh was questioned on the role of Ali, who was an additional security guard posted in the office of the principal, in selling bio-medical waste, including used syringes, gloves and saline bottles.

“We want to know from all accused whether more persons were involved in the financial irregularities,” said a CBI officer.

In a letter to the state vigilance commission on July 14, 2023, Akhtar Ali, a former deputy superintendent at RG Kar, said Ghosh and a few others were involved in several corrupt practices.

Ali mentioned in the letter that a nodal agency that was responsible for transportation of bio-medical waste of RG Kar was not receiving waste in adequate quantity “for the last five-six months”.

Ghosh and a few others, the letter said, ensured that projects worth crores of rupees were awarded to a few favourite bidders who were not even eligible to bid.

Ali’s letter and his subsequent petition in Calcutta High Court led to an order to the CBI to probe the alleged financial irregularities at RG Kar.

Sources said the central agency was also investigating whether Ghosh was instrumental in awarding contracts to Ali, Singha and Hazra.

The agency is also trying to find out whether Ghosh was involved in any malpractice in recruiting contractual employees and misappropriation of academic funds.