The investigators are focusing on criminal groups operating in the area, especially three major gangs -- Hazi Group, Gangchil Group and Babu Group, who might have been angered by the Rab operations in the area.

Detectives yesterday recovered an abandoned trawler, which they suspect had been used by the killers, in Bangshi River about 30 yards off the crime scene.

Meantime, brick fields in Kaundia, where Rab deputy assistant director Humayun Kabir and constable Phool Mia had been shot dead Saturday afternoon, and the adjacent area became deserted yesterday as all the workers had fled the area fearing harassment.

Sub-inspector Nasimuddin of Savar police station yesterday filed a case against unknown killers and the Detective Branch (DB) was tasked with the investigation of the case.

Police yesterday said 24 people rounded up on Saturday were being kept in Rab custody while one was in police custody.

However, neither police nor Rab brought any charge against any of the detainees or shown them arrested in connection with the murders.

Visiting the area yesterday, this correspondent found abandoned blankets, vegetables and other valuables scattered at different brickfields as the workers had fled the area since Rab had started rounding them up indiscriminately following the murders. Although Rab had initially rounded up over 300 people, they later released all but 25.

Members of different intelligence agencies yesterday visited the hut at Tara Mia's brick field and collected evidence, where the two Rab personnel had been dragged before the killers shot them in the head.

A three-member joint probe team comprising members from police, Rab and the Detective Branch, which was formed on Saturday by an order of the inspector general of police, also visited the area, collected evidence, and talked to the detainees.

The committee headed by ASP Motiur Rahman also includes DB Inspector Akhterzuzzaman and Rab Sub-inspector Ibrahim.

Police said the two slain members of Rab intelligence wing might have been killed by the goons of Amzad Hossain, a local criminal and a body guard of a local union parishad chairman, whom Rab had arrested on February 28 acting on Phool Mia's information.

Amzad faces several criminal charges including one for the murder of Aminbazar businessman Abdur Rouf last month.

Humayun Kabir and Phool Mia might also have been killed due to their work to track down drug peddlers' syndicates at Aminbazar.

"Since many criminals of Dhaka take refuge in the area fearing arrest and the two Rab officials were carrying out surveillance on them, some of them might have been enraged and got the Rab personnel killed," said a police officer.

Although, Savar police filed a case yesterday, they refused to disclose the content of the FIR (first information report) when reporters visited the police station in the morning.

Police said they collected some evidence from the spot.

Meanwhile, Sakhina, who used to cook for the workers and had been the first to notice the bullet-ridden bodies of the two slain Rab personnel, was arrested by Rab from her house in Salehpur area Saturday night. She is being interrogated in Rab custody.

Rab personnel yesterday received the bodies of their slain colleagues on completion of autopsies at Dhaka Medical College morgue yesterday noon.

Morgue sources said the killers shot the Rab men in the head point blank. In each of the victims' throats a bullet was found lodged in similar positions. Prior to the killings the victims were tied up.

Investigators suspect that the killers might have sedated the victims before killing them.

Their bodies were taken to the morgue in the early hours of yesterday.

Talking to The Daily Star, Commander Masuq Hassan Ahmed, Rab director of its legal and media wing, said yesterday, "We have yet to ascertain the motive and identities of the killers."

"We've some information in our hands, which we cannot share with you for the sake of capturing the killers."

After the namaj-e-janaza of the murder victims at Rab-1 headquarters, Kabir's second janaza was held in Dhaka Cantonment. Their bodies were taken to their home villages for burial.

Rab DAD Humayun Kabir, who hailed from Bakshichar village in Babuganj, Barisal, joined Bangladesh Navy on December 11, 1980. Kabir was senior chief petty officer of the navy when he joined Rab-11 on May 15 last year. He left behind his wife, a son, and a daughter.

Phool Mia, who hailed from Halidabagh village under Sonatola upazila in Bogra, joined Bangladesh Police on January 4, 1997. He joined Rab-11 on June 4 last year. Phool left behind his wife and a son.