Police said Ullah, an immigrant from Bangladesh who set off a crude bomb strapped to his body in a crowded New York subway passage on Monday, had visited Dhaka after the couple’s baby son was born.
“We are trying to know how he was radicalized and whether he had any associate,” senior counter terrorism officer Saiful Islam told AFP.
He said police had raided the family home in Dhaka and questioned Ullah’s 25-year-old wife, Jannatul Ferdous Piya and her father, but that neither was under any suspicion.
Ullah reportedly told US police investigators he wanted to avenge US airstrikes on the Daesh group and was also inspired by Christmas terror plots in Europe.
Bangladesh police are investigating whether he was radicalized in his Muslim-majority homeland, where foreigners have been among those targeted in deadly assaults claimed by the IS group and Al Qaeda.
Police in Bangladesh say he has never appeared on a watchlist there.
Mofazzal Hossain, caretaker of the family apartment in Hazaribagh in the old part of Dhaka, described him as “pious and a gentleman.”
“He used to pray in the local mosque five times a day. He would urge us to pray and do good work,” Hossain told AFP
“He visited Bangladesh in September after his son was born,” he said, adding Ullah married in January 2016, but did not take his wife to the US.
US authorities say Ullah migrated seven years ago as the member of a family already living there under what is known as “chain immigration.”
His family was originally from Sandwip, an island off Bangladesh’s south coast, but police believe his father moved to Dhaka before Ullah was born.
“We are questioning one of his relatives for more information,” local police chief Noor-e-Alam Mina told AFP.
The impoverished riverine nation of 160 million has been waging a war against homegrown extremism in the wake of numerous attacks by radical groups in recent years.
In July last year militants stormed a Dhaka cafe and massacred 22 hostages, including 18 foreigners, in an assault claimed by the IS.
Security forces have shot dead more than 70 alleged militants in a fierce crackdown since the cafe carnage.
Bangladesh last month arrested an alleged militant from Ansarullah Bangla Team, a homegrown extremist group with links to Al Qaeda, over the 2015 murder of a prominent Bangladesh-origin American blogger in Dhaka.
The secular government of Prime Minister Sheikh Hasina has vowed to root out extremism but says international radical groups do not operate inside Bangladesh.
The Bangladesh embassy in Washington DC condemned the New York bomb attack and restated Bangladesh’s “zero tolerance” approach to extremism.
“A terrorist is a terrorist irrespective of his or her ethnicity or religion, and must be brought to justice,” the embassy said in a statement.