The CBI has started investigating people known to both Sandip Ghosh, former RG Kar principal, and Ashis Pandey, a house staff at the medical college, in its attempt to trace those who were involved in financial irregularities at the government-run facility.

Ghosh and Pandey both are in CBI custody for their alleged links with the financial irregularities. Ghosh is also in custody in connection with the rape and murder of a young doctor at RG Medical College and Hospital on August 9.

Sleuths are scanning the financial transactions from the bank accounts of Ghosh and Pandey over the past year and a half to try and identify those who received payments in tranches from the two, sources in the central investigating agency said.

Details of RG Kar’s bank account, too, have been collected, the sources said.

Officers said they went through Pandey's call details to understand how close he was to Ghosh and some of the associates of the former principal, who resigned days after the rape and murder.

The CBI had on October 3 arrested Pandey after questioning him for several hours at the agency’s office in Nizam Palace in south Calcutta. Sources said Pandey was called for questioning after it emerged that he could be involved, with a few others, in financial irregularities at RG Kar.

Pandey, who is the president of the Trinamool Chhatra Parishad unit at the medical college, had earlier faced CBI interrogators in connection with the rape and murder.

"It appears there was a deal between Ghosh and Pandey. Pandey received illegal payments from vendors associated with the medical college and Ghosh, during his tenure as principal, seems to have backed him,” said a senior officer in the Economic Offences Wing of the CBI.

“The motive behind the deal between the two is crucial to the case. We are trying to find out about those who were involved in the cartel. The extent of benefits the two allegedly enjoyed because of the deal is as much a part of the investigation as the number of people involved in the corrupt practices."

The CBI had arrested Ghosh on September 2 in connection with financial irregularities at the medical college and hospital. Later, he was "shown arrest" in the case of rape and murder.

Besides Ghosh, the CBI had arrested three men on September 2 for their alleged role in the financial irregularities.

They were Afsar Ali, who was Ghosh's additional security guard; Biplab Singha, who supplied medicines and other items to the hospital; and Suman Hazra, who allegedly supplied medicines and medical equipment at inflated rates to the hospital.

Pandey was the fifth person arrested in the case.