LONDON — Details emerged Tuesday of the three London Bridge attackers: a Pakistan-born failed customer service clerk with links to one of Europe’s most prolific hate preachers, a Moroccan pastry chef whose partner said he once went swimming rather than see his daughter and an Italian man who told authorities he “wanted to be a terrorist.”

At least two of the men were known to British intelligence and law enforcement officials, raising questions about whether anything could have been done to stop the attack, which began Saturday when the men drove a rented van into a crowd and then leaped out to stab people who crossed their paths. Seven were killed and nearly 50 wounded. All three of the attackers were shot dead by police.

Security has become a key issue in the run-up to Thursday’s general election. British security officials said none of the men was considered violent, but they acknowledged the difficulty of predicting whether extremists will turn dangerous. The assault was the third attack in three months in which most of the assailants had been on authorities’ radar at some point.

As the investigation expanded to look at how the men knew one another and whether they were part of a larger conspiracy, Pakistani intelligence authorities swooped Tuesday into the town of Jhelum, where Khurum Butt lived until the time he was 7, when he moved to Britain. His cousin, 18-year-old Bilal Dar, told The Associated Press that Butt’s uncle was taken in for questioning. It was unclear if he was detained.

Butt, 27, embraced radical Islam during his time in London and was once filmed in a documentary called “The Jihadis Next Door.” In the film, he was seen with a group unfurling a black-and-white flag associated with the Islamic State group.

Police identified the second attacker as 30-year-old Rachid Redouane, also known as Rachid Elkhdar, who claimed to have both Moroccan and Libyan roots and worked as a pastry chef in Ireland, where he had lived in the past five years as well the east London suburb of Dagenham.

The third attacker was identified as Youssef Zaghba, a 22-year-old Italian national of Moroccan descent who was reportedly working in a London restaurant.