The elite Rapid Action Battalion (RAB) today said the Jamatul Mujahideen Bangladesh women operatives were monitored before the arrests last night.
"We came to know about women operatives from an earlier arrest of a JMB regional chief. We secretly monitored one of them and then arrested the four from different areas of the city," a RAB official said.
One of them is believed to be the recruiter of the gang.
"We secured substantial information about JMB from her phone records," he said.
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The RAB issued a group photo of the four in custody in which the women could be seen in veils covering their faces.
The arrests were the second major success for authorities probing JMB's women activists after the arrest of seven women last month from central Tangail district. Of the seven, at least three were part of "suicide squad", police had said.
"We have identified the fresh suspects by their organizational names so far. Investigations are underway to gather more information about them," Islam said.
The police also claimed to have tracked down Chowdhury and Marzan and "they are staying very much in Dhaka".
On August 12, police unidentified Marzan and Chowdhury. The next day, they named former university teacher Hasnat Karim in the case.