The similarities in the way Niloy and three other bloggers were killed suggest that the same militant outfit might be behind all the four murders, detectives said yesterday.

Separate groups claimed responsibility for the killings of bloggers Avijit Roy, Oyasiqur Rahman and Ananta Bijoy Das this year, but detectives suspect those groups are offshoots of banned militant outfit Ansarullah Bangla Team, said Dhaka Metropolitan Police spokesperson Monirul Islam.  

A group named Ansar Al Islam has admitted through e-mails that it killed Niladri Chattopadhyay Niloy. In this case too, detectives suspect Ansar Al Islam is an offshoot of Ansarullah Bangla Team, he said at a press briefing at the DMP media centre.

Niloy, 28, was hacked to death by four suspected Islamist militants in his rented flat in the capital's Goran on Friday.

According to the autopsy report, he was hacked 14 times, mostly at the upper parts of his body, including neck, throat and head. Avijit, Oyasiqur and Ananta were also hacked at the upper parts of their bodies.

The gruesome killing of Niloy has drawn condemnation from all around the globe, including the United Nations, United States, United Kingdom and rights body Amnesty International.

The Detective Branch (DB) of police took the charge of the investigation from Khilgaon police on Sunday. Niloy's wife Asha Moni filed the murder case on Friday night, accusing four unknown people.

The police had already visited the crime scene, talked with witnesses and were preparing to send evidences to the Criminal Investigation Department for DNA profiling, Monirul said. 

As claimed by the police, the killers left behind a T-shirt and a gamcha (locally made towel) outside Niloy's flat.

The killers took away his Lenovo laptop and Symphony Xplorer smartphone carrying an Airtel SIM, Asha Moni said in the case statement.

Apart from the shirt and the gamcha, investigators collected nine more evidences from the crime scene, said Zia Md Mostafiz Bhuiyan, officer-in-charge of Khilgaon Police Station. 

The Federal Bureau of Investigation offered assistance and inquired whether there was any link between Avijit's killing and the latest one, said Monirul, joint commissioner (DB) of the DMP.

As Avijit was a US citizen, the FBI is interested in his case, he said, adding that it wanted to know whether sorting Niloy case would help indentify Avijit's killers. 

The FBI wants to help in Niloy case as well, Monirul said.

The police have so far arrested three suspects in Oyasiqur killing case. One of them gave confessional statements before a Dhaka court, he added.

Seven suspects, including Ansarullah Bangla Team chief Mufti Jasimuddin Rahmani, were arrested in connection with the 2013 murder of blogger Ahmed Rajib Haider and a charge sheet was submitted in the case in January last year against eight accused, one of whom is on the run.

Detectives have identified seven suspects in Avijit killing case but have not yet made any arrest. Sylhet police have arrested one suspect in Ananta murder case.

Replying to another question, the DMP official urged bloggers not to write anything demeaning religions, which may hurt anyone's religious sentiment.

Both the groups who write derogatory remarks about any religion and who kill people because of such writings are considered extremists, he said.