More than one person was involved in the murder of trader Ganesh Sikdar and his wife Pushpa in their Dum Dum home early on Saturday, said investigators.
The couple had been set ablaze in their bedroom whose door was bolted from outside.
Ganeshs sister-in-law Jharna, the prime suspect, is in police custody. The cops are looking for two more persons, aides of local land sharks who wanted to buy the two-storey house on a five-cottah plot. The area, Surya Sen Pally, has seen a real estate boom in the recent past, owing to its proximity to the proposed Dum Dum-Barasat Metro route.
Jharna has not been co-operating with us but we have found out about two others who might have played important roles in the murder, said an officer of Dum Dum police station.
Jharnas husband Pradyut is a cook in Muscat. She lives on the ground floor of the house with her teenaged son.
The assassins not only set the couple on fire and bolted the door of their room, they also sprinkled kerosene on the staircase leading to the first floor and started a fire there so that no one could rescue them. Jharna alone could not have done everything, said the officer.
The results of the viscera test will confirm whether the victims were drugged before being set ablaze, said additional deputy commissioner (Belghoria) Biswajit Ghosh.
Forensic experts visited the house on Sunday and collected samples from the room and the staircase. There is a possibility that kerosene had been sprinkled on the couple through an open window in the room.
Pradyut, who is expected to return to the city shortly, is also under the scanner, said an investigator.
The cops have not been able to speak to the deceased couples younger daughter Rinki, who woke up around 1.30am on Saturday hearing her parents screams and saw the staircase in flames, because she was still in trauma.
We recorded statements of neighbours who rushed to the house and doused the flames to recover the charred bodies. They told us how Jharna tried to flee immediately after the incident, said the officer.