As the British authorities begin to piece together how their country has fallen victim to three terror attacks in the space of a few months, attention is turning to the backgrounds of the attackers.
Although little is so far known about two of them, one of the perpetrators has left more of a trail.
Khuram Butt was born in Pakistan and raised in London. By the time of his death, he had been brought to the attention of police several times over his extremist views and had even appeared in a documentary about British Islamist extremists called "The Jihadi Next Door."
In the program, he is seen as part of a group unveiling a black flag associated with ISIS in a park in London.
The BBC's Secunder Kermani visited the city of Jhelum, where Butt was born and spoke to some of his family there. The family members said they saw his personality change during two visits back to the family home. During his earlier visit as a young man, Butt was "a typical English boy," with secular interests who liked to hang out with girls. More recently, he had taken an interest in Islam and had begun to grow a beard.
"They noticed a kind of change," Secunder recalled. "He had become noticeably more religious. But they thought this was a positive change. A young man who was aggressive was beginning to calm down and become a bit more patient."
In London, Butt joined a well-known group of extremists, which goes under several names, the most well-known being al-Muhajiroun. A high proportion of British Muslims convicted of terrorism offenses have had some connection to this group or its leader, Anjem Choudary, who has since been jailed. It was during this time that Butt was filmed for the TV documentary about extremists.
In 2015, he was also investigated by the police because of his potential for violent extremism, but the investigation was closed due to lack of evidence of any active plot. Two people near his home in London have claimed to have reported him for hanging around a local park attempting to convert young boys to extremist interpretations of Islam.
What remains unclear is how Butt moved from being associated with al-Muhajiroun to actively planning the assault on London Bridge. It does not appear that his fellow attackers, Youssef Zaghba, a 22-year-old Italian of Moroccan descent, and Rachid Redouane, of Moroccan-Libyan origin, had connections to al-Muhajiroun or Choudary.
"It seems that he moved away from the [al-Muhajiroun] clique after a year," says Kermani. "It seems this group perhaps was a steppingstone for him before he went on to form a more secretive bond with others who planned his attack."
In Pakistan, the news of Butt's crime has devastated his family. His mother apparently recognized her son's body from TV coverage. His uncle sent a message to the victims and their families. "I condemn this incident, this brutal action," he told the BBC. "Even if I don't know [the victims'] names or their nationalities, they're my relatives, my brothers. Why were they killed?"
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