Story highlights London attacker Khuram Shahzad Butt appeared in a 2016 Channel 4 documentary called "The Jihadis Next Door"

At the time of the attack, Butt worked as a receptionist at a fitness center in Ilford, a friend from the gym said

(CNN) Khuram Shahzad Butt, a 27-year-old British national born in Pakistan who died in a hail of police bullets Saturday night after the London attack, was a tall, lanky, straggly bearded young man of few words -- a brainwashed follower of al-Muhajiroun, a loose grouping of British extremists supportive of ISIS linked to a large number of terrorist plots involving UK nationals.

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CNN's Sandi Sidhu met him several times while reporting on the group in the United Kingdom between 2014 and 2016. He went by the name "Abz" or "Abu Zaitun" and seldom spoke during meetings. He was content to leave the task of proselytizing to louder, older members of the group, according to Sidhu.

Khurah Shazed Butt, left, and Rached Redouane have been named as two of the London attackers by the Metropolitan police.

Butt, who lived in Barking in east London, appeared several times in a 2016 Channel 4 documentary called "The Jihadis Next Door," which profiled a group of individuals linked to al-Muhajiroun in the United Kingdom. At one point in the documentary, he can be seen helping unfurl a black banner in Regent's Park after a radical preacher promised it would fly one day over 10 Downing Street. The flag was different in form to the one most commonly used by ISIS.

A friend of Butt's identified him to CNN as appearing in the documentary. Neighbors living beside the residence raided by police in Barking also identified Butt from a still frame in the documentary.

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