This fact came to light during investigation of the respective roles of the six arrested JMB militants.
"He (Farooq alias Inam) was looking after the financial part of the outfit and being the head of the JMB's West Bengal unit, he is the most important among the six arrested," a senior officer of the Kolkata Police said.
Farooq, a resident of Bangladesh's Jamalpur, was carrying a laptop at the time of his arrest from the border area of Bongaon in North 24 Parganas.
A diary was also recovered from Farooq's possession in which the outfit's "tree" in West Bengal is jotted down.
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He is wanted in connection with several cases in the neighbouring country.
"That will be quite crucial but most of these names can be pseudonyms," the IPS officer said.
On Maulana Yusuf aka Yusuf Sheikh, described as the second man-in-command of the JMB's unit in the state, he said, "Going by hierarchy, this person was definitely another important man. Many of the madrasas in West Bengal were under his supervision. He was the chief motivator and had visited madrasas in Simulia a couple of month's ago.
Police officials said they were in touch with their counterparts in Bangladesh and a team of the National Investigation Agency (NIA) also visited the Kolkata Police headquarter at Lalbazar.
On their mode of communication, the officer said they used messengers to pass on instructions and never used Facebook or any other form of social media to communicate.
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Besides Farooq and Yusuf, the STF arrested four others- Shahidul Islam, Md Rubel, Abul Kalam and Jahidul Islam.
Another STF officer claimed that Jahidul was picked up in June for possessing high quality fake currency and during subsequent investigation, it came to light that he was involved in the Khagragarh blast case.
Out of the six arrested from West Bengal and Assam, five were wanted in connection with Khagragarh blast of October 2, 2014 and named in the NIA chargesheet.
Forged identity documents, a white powdery substance weighing around two kg, one laptop, mobile phones, detonator, wire-cutters, batteries, Bangladeshi and Indian currencies, letters written in Bengali, travel guide, books on chemicals and memory cards for camera were seized from them.