The JMB threat is still there as two of its key leaders slipped through police fingers during a raid into a JMB "bomb and ammunition factory" in Mirpur on Friday.

According to the statement of the case filed in this connection, JMB second-in-command for Dhaka region Sohel Rana Hiron and trainer for bomb and grenade making Mostafizar Rahman had cleverly fled the scene blending into tenants who were being taken out of the Mirpur building.

It said Hiron and Mostafizar slipped away pretending to be tenants after the raid at the "factory" when law enforcers were evacuating the tenants from the six-storey building. The "factory" was in a flat on the fifth floor.

Some police officials said the two militants would remain a threat until they were caught. None of them would go on the record with The Daily Star.

But DB Deputy Commissioner Mashrukure Rahman Khaled claimed that they would not be a big threat since they were on the run.

In the 15-hour crackdown, detectives seized 16 improvised grenades, other ingredients for making over 200 bombs and grenades, a suicide vest, and 15 bullets.

They also arrested three suspects.

Detectives said Hiron and Mostafizar were key leaders of a faction of Jama'atul Mujahideen Bangladesh (JMB), which was allegedly involved in some recent attacks, including the one at Hossaini Dalan and two police checkpoints.

Joint Commissioner of the Detective Branch (DB) of police Monirul Islam said Hiron took over the charge of the operations commander of the faction after his predecessor was killed in a "shootout" with detectives last month.

Mostafizar has a diploma in electrical engineering.

Apart from training new recruits at the Mirpur den, Mostafizar used to visit different areas of the country to train recruits and make bombs and grenades as per the organisation's requirements, the police official said.

The JMB faction had at least 60 active operatives and over 100 supporters. Of them, 15 to 20 were diehard activists and eight to 10 of them were capable of making bombs and carrying out attacks, investigators claimed.

The faction's main source of funding was robberies and muggings, they added. They, however, did not disclose the name of the chief of the faction.

The faction members became inactive amid leadership disputes following the execution of its chief Shaekh Abdur Rahman and a number of other organisers.

They became active towards the end of last year and early this year after the inclusion of some operatives from pro-Jamaat-e-Islam student body Islami Chhatra Shibir and different radical Islamist organisations, they claimed.

They claimed that sometimes grenades or bombs were supplied from the Mirpur factory while other times Mostafizar would travel to destinations to make the bombs.

They also said the grenades used at the shia congregation at Hossaini Dalan and those recovered at the JMB den in Kamrangirchar were similar to those found in Mirpur.

A top DB official also said the pipe bombs seized in Mirpur had similarity with those used in the bombing of a mosque at the naval base in Chittagong recently.

Monirul said, "A good number of JMB members recently arrested in the northern region were members of this JMB faction."

Around 35 members of the faction have so far been arrested, according to detectives.

DB inspector Shafiuddin Sheikh of the bomb-disposal unit on Friday filed a case against five identified JMB members, including Hiron and Mostafizar.

The other three arrested suspects were: Abu Sayeed Russell, 22, a fourth year student of East West University, Mohammad Elias Omar Faruk, 23, who hails from Matlab in Chandpur, and Mohsin Ali Rubel, 20, of Komor village in Joypurhat.    

Russell, who is also a coordinator of the outfit, was capable of making improvised grenades. Hailing from Kotwali of Dinajpur, he joined JMB two years ago. He also played the role of a researcher to find out tactics to avoid arrest, law enforcers claimed.

Five to six unknown militants were also accused in the case filed under the Anti-Terrorism Act.

A Dhaka court on Friday placed the three suspects on a six-day remand each for interrogation.