The Islamic State has for the first time identified Canadian citizen Tamim Chowdhury as its former head of military and covert operations in Bangladesh — using his real name in print, in an unusual move — six weeks after he died in a hail of bullets during a shootout with Bangladeshi police.

Chowdhury, a relative unknown until this year, gained worldwide notoriety in July as the alleged mastermind of a terrorist attack on a popular Dhaka cafe that left 22 people, mostly foreigners, dead. ISIS immediately claimed responsibility for the attack, but until Tuesday the extremist group had never acknowledged any association with Chowdhury.

"I think it's the first time that ISIS has ever used anyone's real name in an official publication," said Amarnath Amarasingam, a fellow at the Center for Cyber and Homeland Security at George Washington University who has written extensively on extremism.

Chowdhury was killed in August in one of a series of raids on suspected militant dens in Bangladesh, which has seen dozens of deadly attacks on atheists, secular writers, and religious minorities in the last two years.

The latest issue of Rumiyah magazine, a newer publication hawked by the militants, includes a fresh account of the Dhaka attack, under Chowdhury's byline. The author profiles each of the six attackers who died in the clash and describes the bloodshed as "just a glimpse, and what is yet to come by the permission of Allah will be worse and far more bitter."

He says the Holey Artisan Cafe, located in Dhaka's diplomatic quarter, was chosen because it was a "sinister place" where "crusaders would gather to drink alcohol and commit vices through the night."

In an interview, Bangladesh Police Chief Shahidul Hoque said he believes Chowdhury, age 30 when he died, was behind every aspect of the restaurant operation — recruiting the young men who carried it out, training and advising them, providing them weapons and explosives, and giving them religious counseling.

That's a far cry from the mild-mannered student whom friends in Windsor, Ontario, recalled as possessing "no leadership qualities" and who was deemed "most likely to become a scholar" in his high school yearbook.

His parents, Shafi Ahmed Chowdhury and Khaleda Shafi Chowdhury, settled their family in the Canadian border city across the river from Detroit shortly after Bangladesh's brutal independence war, according to police. Relatives told Bangladeshi media that his grandfather played a part in the anti-liberation movement.

But Tamim never saw any of that unrest. He developed into a bright young man who excelled academically. In high school, he was involved in everything from the tennis team to the yearbook club.

"I would like to thank all my friends, teachers, and coaches for their wonderful support throughout the last four years. Remember, Spartans: You will only go as high as your expectations! So aim higher and work hard," wrote Chowdhury in his earnest 2006 senior-year farewell to classmates.

'I think it's the first time that ISIS has ever used anyone's real name in an official publication.'

"He was absolutely brilliant," said Chris Woodrich, who attended the now-closed J.L. Forster Secondary School with Chowdhury. He described him as a quiet guy with a genuine-looking smile, who seemed mainly focused on his studies, who showed interest in Islam only during Friday prayers — he'd go to the school's music room, where a musallah had been set up. "We were basically a nerd squad. We'd sit there in the auditorium and play chess at lunchtime," said Woodrich.

"I don't remember seeing him ever getting in trouble for anything," Woodrich added.

A former teacher wrote on Facebook that Chowdhury was "very respected" and well-liked.

"He wasn't bullied. Didn't seem to struggle," the teacher, who has since deleted the comment, said.

The quiet manner extended beyond the school walls.

"He would come to prayers, read, and leave," said one imam at Windsor's West Musallah mosque, the smallest of several religious hubs in the community of 30,000 Muslims, around the corner from the high school. "I honestly never saw him interact with a single person."

Amarasingam first heard of Chowdhury from friends of Ahmad Waseem, a man who left Windsor in 2013 to join the Islamic State and who was likely killed in battle in 2015.

Sometime between 2011 and 2012 he moved to Calgary, Alberta, possibly to work at a large engineering firm.

Shaikh Navaid Aziz, imam at Calgary's 8th and 8th Musallah, first met Chowdhury in 2009 while teaching a class at the University of Windsor.

"He attended the class and he was very quiet, very laid-back," said Aziz, noting, however, that Chowdhury was highly intelligent and would pick things up quickly. "He would pass under the radar and you wouldn't even notice him."

The two wouldn't see each other again until 2012, when Aziz took a job at the Islamic Information Society in Calgary. He emerged from a Friday sermon in April of that year to chat with people outside and saw Chowdhury among them.

"I was shocked," Aziz recalled. "I was like, 'Hey, what are you doing here?' and he completely blanked me. He pretended as if he didn't know me at all."

"Now, what's interesting about this interaction is he was with Damian Clairmont," he said, referring to a Canadian-born Muslim convert who travelled to Syria to fight with al-Qaeda-linked Jabhat al-Nusra, to his death.

Clairmont was one of six men who formed a study circle at the 8th and 8th Musallah before leaving Canada to fight for extremists.

Apart from that one interaction, there's no evidence Chowdhury was part of the same study circle Clairmont and the five other Canadian jihadis had formed at the 8th and 8th Musallah. Aziz said no one he's asked remembers this being the case, and Chowdhury isn't in any of the video footage from that time.

"The question is what happened before [Calgary], and who he met and who he talked to," said Amarasingam.

A vigil for the 22 victims of the July attack at a cafe in Dhaka, Bangladesh, that was masterminded by Tamim Chowdhury. (AP Photo)

While some news agencies are reporting that Chowdhury had been trained in Syria, Hoque, the police chief, said investigators have yet to verify that. What they do know is that he entered Bangladesh in October 2013 from Dubai.

Either way, Chowdhury's rise to the top was swift, police said. According to Bangladeshi authorities, he'd been leading the Jama'atul Mujahideen Bangladesh, a group that authorities once thought they'd wiped out, since it reorganized in 2013 and began recruiting educated young men from upper-middle-class backgrounds, carefully selecting targets, and assassinating them with machetes and other sharp weapons. The militant group has pledged its allegiance to ISIS.

Since his death, other ties between Canada and extremist outfits in Bangladesh have emerged: One of Chowdhury's accomplices, a now-dead former army officer named Mohammed Jahidul Islam, once received training from the Canadian military. (Canada's Department of National Defence confirmed to VICE News that someone of a "similar name" participated in an academic course on warfare.)

Chowdhury's family has kept a low profile through all this. Except for an uncle who identified the body, no one has laid claim to what remains of the alleged mastermind. Even the Bangladeshi police haven't been able to reach Chowdhury's parents about retrieving their son's body, Hoque said.

When Md Abdul Quaiyum, president of the Bangladesh-Canada Association, Windsor-Essex, tried reaching out to Chowdhury's parents, who still live in Windsor, they distanced themselves from their son. They said he was grown, had acted on his own accord, and that they hadn't been in contact with him since he moved to Calgary.

Contacted through Quaiyum, they declined VICE News' interview request.

"They hoped [Chowdhury] would provide for the family," said Quaiyum. "And then something like this happens. Understandably, they're in a lot of pain. That's why they don't mix with anyone."