"We have arrested Sheikh Sadiq alias Sajid's brother Mohammad Monayem from Farazikanda in Narayanganj early this morning," a RAB spokesman told newsmen.
The elite anti-crime Rapid Action Battalion (RAB) arrested Monayem three days after the West Bengal police nabbed Sajid, a member of Bangladesh's banned militant outfit Jamaatul Mujaheedin (JMB), while the National Investigation Agency (NIA) earlier described him as the "chief of the Burdwan module".
Sajid is the son of a retired Lieutenant of Bangladesh army and a resident of Narayanganj district, NIA had said.
Indian police earlier arrested a number of people, two of them being women from West Bengal and Assam, in connection with the blast on October 2.
JMB and other Bangladesh-based militant groups like Harkat-ul-Jihad-al-Islami (HuJI) seemed to have suffered a setback in view of years of massive security clampdown but reports often suggest they are trying to regroup.
In recent years, the group has carried out a series of bomb attacks across Bangladesh killing scores of people including two judges prompting the launch of a massive anti-terror campaign while officials have also suggested they had their organisational network in West Bengal.