The investigators also found the family members of the dead to be very 'suspicious'. The investigating officer (IO) of the case termed the murders 'mysterious' and suspect the family was involved in illegal activities.

Meanwhile, the identity of one of the three dead was known yesterday. Victim Ajay Singh is the uncle of Sanjay, a student of Milestone School and College, who was also killed on Thursday. The identity of the male domestic help, the third victim, is yet to be known.

Law enforcers found the bodies of three men of Manipuri community at a house in Uttara Thursday night. All the bodies had their throat slit. Police yesterday sent the bodies to Dhaka Medical College morgue for autopsy.

Police held Kuleswar Sinha, father of Sanjay, at Uttara Police Station for quizzing after he went there to receive his son's body yesterday evening. Uttara police also picked up three, Ashit Kumar, Jisair and Lipson, for quizzing.

Law enforcers held Kuleswar on May last year after six National Liberation Front of Tripura (NLFT) insurgents were killed in an encounter with Rapid Action Battalion (Rab) in a tea estate in Kamalganj of Moulavibazar.

He was then held for allegedly providing shelter to the six insurgents. Intelligence agencies now suspect the three murders could have been committed by people connected with those six insurgents.

Meanwhile, the IO of the case also alleged that Rab, who went to the spot first and seized some evidence, are not cooperating with him. Sources said Rab seized three cartons and a computer from the house.

"They [Rab] reached the house an hour and a half before police reached there. They did not even mention about the seizure and now they are not sharing the information they have about the killing," said IO of the case Sub-Inspector (SI) Jalil of Uttara Police Station.

About Sanjay's father, the IO said, "Kuleswar could be involved in some kind of illegal activities as he tried to take away the bodies even before filing a case." Kuleswar, who claimed to have a loom business, hails from Kamalganj in Moulavibazar.

There must be at least three people involved in the killing as it's not possible for one to kill the three, said the IO.

Moulavibazar sources said Sanjay had only one brother and a sister, although the owner of the building earlier said Sanjay came with two of his sisters while renting the flat on the fifth floor of the building last year.

The police are now looking for Sanjay's cousin Sumon, who used to live with him, to learn more about the killing as he was at the house the night before the killing took place. He also informed Sanjay's father about the murders. They are also looking for two of Sanjay's sisters which the building owner claimed Sanjay had.

The guards said Sumon left the house around 6:00am in the morning and came back around 10:00am but did not go into the flat. He took the car he and Sanjya used to use and left the house.

Rab officials are yet to disclose their source and findings about the killing for the sake of investigation. They however did not rule out the link of insurgency with the triple murder.

No cases were filed until 2:00am last night, said the duty officer of Uttara Police Station.