Birmingham, Britain’s second-biggest city behind London, has produced a disproportionate number of convicted Islamist militants, including some linked to the Sept. 11 attacks, and to last year’s bombings in Brussels.

Mr. Masood, who converted to Islam in his late 30s, was born and raised in an affluent village in southeast England. He spent much of his adulthood in and around London, interrupted by jail time and two yearlong relocations to Saudi Arabia. But Birmingham was his last residence.

Birmingham was the birthplace of Britain’s first suicide bomber, the residence of a financier of the Sept. 11 attacks, and the place where Al Qaeda hatched a plot to blow up a commercial airliner in 2006. When a masked member of the Shabab, the Somali extremist group, celebrated the murder of the soldier Lee Rigby in a 2013 video, he listed Birmingham as the first source of its fighters.

The man who is believed to have recruited the militant known as Jihadi John, the Islamic State executioner with the King’s English accent, was from Birmingham, as was his closest associate. Other prominent militants who have come through the city’s underground networks include Abdelhamid Abaaoud, organizer of the 2015 Paris attacks, and Mohamed Abrini, a Belgian national who helped plot the 2016 Brussels attacks. In 2014, Birmingham was at the center of a so-called Trojan Horse plot in which, it was alleged, a group of Islamist extremists had sought to infiltrate and take over two dozen state schools.

One man in Britain who blurred the boundary between religion and violent extremism is Anjem Choudary, a founder of Al Muhajiroun, which is classified as a terror organization. Mr. Choudary, who is now in prison after he was convicted last year of encouraging support for the Islamic State, had preached in Birmingham several times in recent years.

“They turned religion into a gang-type thing, with thugs around him saying, ‘Come join our gang,’” said Mr. Ashfaq, the director of Kikit. Their message, he said, was “you can be cool, you can become a gangster jihadi.”

Read more: New York Times