Asif Mohammad, the 19-year-old youth who had allegedly killed his family members in front of his elder brother Arif, had managed to stop him from spilling the beans for four months by allegedly blackmailing him.

Arif, 21, had been following his younger brother’s instructions all along and kept his mouth shut despite having full knowledge about the brutal killings of his parents, sister and grandmother.

Last week, unable to sustain the pressure, he reported the four-month-old incident to Kaliachak police and led to Asif’s arrest.

A senior officer said: “Asif had this tendency to bluff around and pretend that he knew much more than he actually did. He used the same trick on his elder brother and managed to stop him from reporting to the police for four months through blackmail.”

Malda police are also probing Asif's year-long absence from his hometown after he cleared his class X exams, sources said.

Asif Mohammad had disappeared “for a long period” after his Madhaymik examination in 2019 apparently without informing his parents anything about his destination.

Alok Rajoria, superintendent of Malda police, said: “It has been found that he was in Shillong, Meghalaya, for some days. We are probing his activities during his absence and also the people he had interacted with.”

The police said they were trying to ascertain the purpose behind the newly-constructed building adjoining the home.

“It is a peculiar 70-feet high building spread over 2000sqft area. The upper storey has a balcony but there is no staircase. This building was connected with the main building through a tunnel,” said a police officer.

The investigators said they would examine the masons and labourers involved in the construction and try to find out the thought process behind building the house which was totally planned by Asif.

“We know Asif was involved in the building’s design and the masons could provide us with a clue,” said an officer.

Arif, Asif’s brother, has apparently failed to throw any light on the reason to construct a building like this. Arif had blown the lid off the killing of their parents Jawad Ali, 53, and Ira Bibi, 39, sister Rima Khatun, 16, and grandmother Aleknoor Bewa, 73 on February 28.

The police said Asif was in touch with Arif and was in control of the latter’s actions to ensure that he never reported the multiple killings to the police. However, Arif had failed to sustain the pressure and informed the police about the incident.

The police had till now seized five 7mm pistols, 84 rounds of cartridges and 10 magazines from Asif’s friends Sabir Ali, 18 and Mohammad Mahfuz, 20, on Saturday, along with more than Rs 2 lakh in cash. Both the arms and money are believed to belong to Asif, the police said.

However, the cops are yet to ascertain why Asif was keeping the cache of arms and ammunition in his possession.