A couple in their 20s were arrested in Sonarpur on Saturday night for the alleged murder of the woman’s 75-year-old grandmother and a 25-year-old specially abled grandson of the elderly lady.
The couple — Sushmita and Susanta Das — allegedly disposed of the bodies in the septic tank of the elderly woman's house in Sonarpur's Jagaddal.
Police said the couple, who have a baby a few months old, had been living with the victims for a few months.
"Ganga Rani Das, 75, and Manas Ranjan Das, 25, alias Bittu, were killed at least a month ago. But the murders were detected late on Saturday," said an officer of Sonarpur police station.
"Ganga Rani Das is the maternal grandmother of Sushmita Das, one of the prime suspects of the twin murders."
Manas Ranjan is the son of Ganga Rani's son. Both his parents had died and he stayed with his grandmother.
The victims were last seen at their Jagaddal home during Durga Puja, the police learnt from neighbours.
It is suspected that the grandmother-grandson duo were killed two days after Dussehra and their bodies were dumped inside the septic tank of the house.
The lid of the tank, which needs to be opened for cleaning from time to time, was permanently sealed with cement.
The sealed lid aroused the suspicion of some relatives, who had been worried over the disappearance of the elderly woman and her grandson.
“A few days ago, some relatives of the woman came to visit her at her home. But her granddaughter Sushmita did not entertain them. On Saturday, some of the relatives visited the house again suspecting foul play," said an officer of Sonarpur police station.
"Sushmita and her husband tried to fob them off saying Ganga Rani Das and Manas Ranjan Das were not at home. But they accused the young couple of causing the disappearance of the elderly woman and her grandson."
The relatives and some neighbours then saw that the opening of the septic tank in the house had been sealed with cement and became suspicious.
“The relatives and neighbours then broke the seal and found the bodies. They then alerted the police,” said the officer.
The police said after questioning Sushmita and Sushanta that the primary motive of the murder appeared to be ownership of the Jagaddal house. A complaint of torture that Ganga Rani Das had earlier lodged against Sushmita was also another reason for the murder.
“It appears the accused had a lot of grudge against the elderly woman. She had also not approved of Sushmita’s marriage to Sushanta,” said an officer in the Baruipur police district.
The couple were arrested on Saturday and charged under IPC sections dealing with murder, causing disappearance of evidence and common intention.
The bodies have been sent for post-mortem.