The man, a teacher at a private university in Dhaka, had returned to Bangladesh recently after living nearly 20 years in Britain.
Some of the hostages rescued from the weekend attack on an upscale restaurant in Bangladesh's capital were being questioned Monday by investigators searching for clues about the possible masterminds behind the gruesome attack that left 28 dead, including many foreigners.
Authorities were still holding five of the 13 hostages rescued when commandos stormed the restaurant in Dhaka's diplomatic zone Saturday morning, killing six of the attackers and capturing one, according to officials.
Bangladesh's police chief A.K.M. Shahidul Haque said authorities would be interrogating two men, including a suspected militant, who were detained during Saturday's operation. He would not say whether either had been among those counted as hostages, only that they were being treated in a hospital for unspecified injuries.
It was not clear if all five were suspects, or if they were being held and questioned simply because authorities thought they might offer useful information in tracing the origins of the attack.
The official, speaking on condition of anonymity, confirmed investigators were also speaking with a third man described by local media as a Bangladeshi who was trapped inside the restaurant along with his wife and two children. The man, a teacher at a private university in Dhaka, had returned to Bangladesh recently after living nearly 20 years in Britain.
Some photographs and several crude videos taken from an apartment near the Holey Artisan Bakery show the man talking to someone while attackers allowed him to leave before paramilitary forces launched the rescue operation on Saturday. The man's friends and police also said the one of the attackers was a student in the same department at the university where the man teaches.
The brutality of the attack - the worst convulsion of violence yet in the recent series of deadly attacks to hit Bangladesh - has stunned the traditionally moderate Muslim nation and raised global concerns about whether it can cope with the increasingly strident Islamist militants.
Prime Minister Sheikh Hasina's government says the attacks are being carried out by domestic militants bent on imposing Islamic rule, and blames the political opposition of backing the attacks in order to create chaos in the country.
Meanwhile, Indian states that border Bangladesh were on high alert Monday, with the police checking vehicles crossing the shared 4,000-kilometer (2,500-mile) border in case any militants were trying to flee, according to the head of India's paramilitary Border Security Force.
Family and friends of 19-year-old Tarishi Jain, meanwhile, gathered in the New Delhi suburb of Gurgaon as her body arrived for a ceremonial cremation.