A number of Libyans from Manchester have waged jihad abroad, according to Raffaello Pantucci, a terrorism expert at the Royal United Services Institute in London. The Qaeda-linked Libyan Islamic Fighting Group had a contingent in Manchester, Mr. Pantucci said. And in 2010 and 2011, as the anti-Qaddafi uprising in Libya intensified, a number of Libyan-Britons left Manchester for Libya as foreign fighters, he said. More recently, he said, a cluster left for Syria.

In Fallowfield, a neighborhood south of the Manchester city center, residents recalled Mr. Abedi as quiet, respectful and passionate about soccer, often wearing a T-shirt with a Manchester United emblem.

Officials at the Manchester Islamic Center, also known as Didsbury Mosque, where the Abedi family worshiped, have condemned the attack, but declined to talk about the family.

“The horrific atrocity that occurred in Manchester on Monday night has shocked us all,” a mosque trustee, Fawzi Haffar, told reporters.

In 2015, according to a neighbor who spoke on the condition of anonymity over concerns about safety, an imam at the mosque, Mohammed Saeed, delivered a sermon condemning terrorism for political causes. The sermon prompted a heated discussion among congregants and some, including Mr. Abedi, objected to it.

“He was angry,” the neighbor said. “He scared some people.”