Neo-Jamaat-ul-Mujahideen's wanted leader Nurul Islam alias Marjan and another unidentified extremist were killed by Counter-Terrorism and Transnational Crime unit in Mohammadpur Beribadh area of the capital.
"A seal from a factory in Bihar was found on the three AK22 rifles recovered after the Gulshan terror attack," Counter-Terrorism and Transnational Crime chief Monirul Islam was quoted as saying by the Dhaka Tribune.
The move came amid media reports that militants, especially members of the Islamic State, are popping addictive pills, which help "fuel their fury", before attacking the victims.
Former captain Abdul Majed was hanged for his involvement in the 1975 coup in which the country's founder Bangabandhu Sheikh Mujibur Rahman was assassinated, nearly four-and-a-half decades after the high profile massacre.
Canadian-Bangladeshi Tamim Ahmed Chowdhury and his two associates were killed during an encounter at the militants' hideout.
Counter-Terrorism and Transnational Crime chief Monirul Islam said they got information that Jamaat-ul-Mujahideen Bangladesh chief Musa along with some other JMB terrorists are in Sylhet.
Six people including two police officers were killed in twin blasts. The dead included two police inspectors and four onlookers, two of them being college students.