The district police has transferred the case to the CID, official sources said.
CID and forensic experts had visited the residence of the doctor and spoke to his widow yesterday, they said, adding that a forensic team from Kolkata also collected samples from his house.
According to the FIR lodged in the case, Bikram Saha, an assistant professor at Midnapore Medical College and Hospital, had committed suicide by taking an insulin overdose on June 9 and had died in a private hospital in Kolkata on June 13.
His widow had complained that Saha was allegedly 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.
Saha was suffering from depression and was declared a psychiatric patient by a board of doctors at the hospital, she had said.
Sarkar, who heads the charitable organisation hospital, has denied knowing the doctor.
Hospital sources claimed that Saha had not attended the hospital for the past three years due to his illness.