In a plot straight out of a crime thriller, Malda killings accused Asif Mohammad had allegedly lured his family members into a tunnel in the house on the pretext of clicking their photos and then drowned them inside a wooden structure, police said on Sunday.

The Bengal Police suspect that a property- related dispute might be one of the reasons behind the killings in Gurutola village in Kaliachak but says it is not conclusive yet as further investigation is underway.

Asif's friends Sabir Ali (19) and Mohammad Maruf (21) were arrested for possessing five 7mm pistols, 80 cartridges and 10 magazines allegedly given to them by the murder accused a week ago, Additional Superintendent of Police, Malda Rural, Aneesh Sarkar said.

"However, 19-year-old Asif is the only accused person in the killings. No links have been found between the firearms and the murders. We are trying to find out from where he had procured the pistols and cartridges," Sarkar told reporters.

Based on a complaint lodged by the murder accused's elder brother Arif Mohammad, police arrested Asif after exhuming four bodies from a room in their house in Gurutola village on Saturday.

Preliminary investigation suggests that on February 28, Asif had spiked the cold drinks of his father Jawad Ali (50), mother Ira Bibi (45), sister Arifa Khatun (17) and grandmother Alekjan Bibi (75) with some stupor-causing drugs or sleeping pills and made them drowsy, he said.

"On the pretext of clicking their photographs, Asif then led them into a tunnel that he had dug in the house and made them lie inside a wooden structure he had constructed. He then gagged their mouths and tied their hands with duct-tapes and finally filled the structure with water and drowned them, before burying their bodies," the officer said.

"The accused had taken a lot of money from his father and was demanding that the entire property be written in his name. Prima facie, it seems that a property-related dispute might be one of the reasons behind the murders but that is not conclusive yet as further investigation is underway. A cash amount of over Rs 2 lakh has also been seized," he said.

The accused's elder brother had managed to escape from the spot as the effect of the drug was less on him. He had changed locations for four months, before informing the police about the incident on Friday night.

"We have examined Arif but did not find anything suspicious. Asif had attempted to kill his brother too but he somehow managed to escape. The accused used to continuously threaten his elder brother as a result of which, he did not speak about it for four months. He finally mustered courage and approached the police," Sarkar said.

Several electronic gadgets have been seized from the house and police are investigating all angles to ascertain the motive behind the murders.

Asif has been booked under Section 302 (murder) of the IPC and Arms Act. His two friends have been booked under Arms Act. The trio will be produced before the court during the day and their police custody will be sought, he added.