Post-mortem findings seem to confirm the police suspicion that Mridul Kanti Das had killed his wife, daughter and a nonagenarian member of his family before hanging himself early on Monday.

The 63-year-old, suffering from depression, is believed to have killed all three in a fit of rage for no apparent reason, said an officer.

The cops are, however, not sure when the Haridevpur residents died and whether the three who were murdered had been drugged.

“We are waiting for the forensic and viscera reports which will reveal whether the three were under the effect of any sedative,” said S. K. Choudhary, the additional superintendent of police (industrial), South 24-Parganas.

The sleuths have also not yet ruled out the involvement of an outsider in the crime, though the door of the house was locked from the inside.

U.P. Ghosal, the doctor who conducted the post-mortem, said: “Judging by the posture of Mridul’s body, it is clear that he was not murdered. The wounds on the other three were ante-mortem (before death) in nature.”

Mridul was found hanging by a towel from the ceiling fan of his first-floor room on Monday morning.

The bodies of wife Nibha and daughter Anindita, with wounds on their necks, were in adjoining rooms on the ground floor.

Nibha’s 94-year-old maternal uncle Anil Kumar Ghosh, who lived with the family, was found dead in Anindita’s room, his face bloodied.

The cops suspect Mridul had used a chair, found upturned in a corner of the room, to reach the fan.

An investigating officer said Mridul was under the treatment of a psychologist. According to a prior arrangement, the husband of his elder daughter, who was unaware of the tragedy, had turned up at the Haridevpur house around 10am on Monday to take Mridul to the doctor.

Mridul was also hard of hearing and an introvert. “It’s not unusual for a person suffering from hearing impairment to be a little suspicious.... An introvert tries not to express his feelings but if pushed to the limit, the pent-up anger explodes. This might have happened with Mridul, too,” said the officer.

Relatives and neighbours said Mridul mostly kept to himself.

Nibha’s brother Salil Biswas, who lives next-door, said Mridul rarely visited his home. “He last came on March 1,” said Biswas.