Bangladeshi authorities named a third prime suspect on Monday in their investigation into the July 1 attack at a Dhaka cafe in which 20 hostages were killed, most of them foreigners.
Mohammed Saiful Islam from Dhaka's counter terrorism police said Nurul Islam Marjan, a commander from the Jamaat-ul-Mujahideen Bangladesh (JMB) militant group, had been identified on information from several different sources.
"We got this details and now we are verifying these information," Saiful, a senior officer, told Reuters.
Police have accused JMB of several attacks over the past 18 months that have ratcheted up fears about militancy. JMB says it is affiliated to Islamic State but the government insists Islamic State has no presence in Bangladesh.
On Thursday, police arrested five members of an Islamist militant group who, they said, were planning suicide attacks in the capital and counter terrorism chief, Monirul Islam, said the third prime suspect had been identified.
Police officers had swooped on a cell on Thursday in the outskirts of Dhaka and said the suspects, including four would-be bombers and a bomb-maker, had been sent to the capital to bolster the JMB's attack capability.
They were all from the northern part of Bangladesh.
Marjan had disappeared from his family's village in the northern Pabna district, 160 km (100 miles) from Dhaka, eight months ago and was studying Arabic at Chittagong University, police said. His father has been detained, they said.
Islamic State claimed responsibility for the cafe attack and, while the government has dismissed the claim, security experts say the scale and sophistication of the assault suggest links to trans-national networks.
Police say Tamim Ahmed Chowdhury, a Canadian citizen and the prime suspect, is still at large in Dhaka. Analysts say Islamic State identified him in April as its national commander.
Police are also still hunting for a sacked army major-turned militant, Syed Mohammad Ziaul Haque, as part of the investigation.