Police said the district police transferred the case to the CID during the day.
CID and forensic experts had visited the residence of the doctor and spoke to his widow yesterday.
The forensic team from Kolkata had collected samples from the house, official sources said.
Bikram Saha, an assistant professor of Midnapore Medical College and Hospital, had committed suicide by taking an overdose of insulin injection on June 9 and had died in a private hospital in Kolkata on June 13, the FIR said.
The widow had complained to the police that he was tormented by CPI-M state committee member Dipak Sarkar and six doctors of the medical college who were forcing him to work in a paramedical centre run by a charitable organisation.
This had caused mental depression for Saha, she said.
He was declared a psychiatric patient by a board of doctors in the hospital.
The charitable organisation is headed by Sarkar, who has, however, said he did not know the doctor.
Hospital sources said he had not attended the hospital for the past three years due to his illness.
