One of the London Bridge knifemen had been reported to the anti-terror police over fears he was attempting to radicalise schoolchildren, according to reports.
The suspect was reportedly said to have become radicalised after watching extremist videos on YouTube.
Residents at the Elizabeth Fry flats in King’s Road, Barking - where a number of arrests were made on Sunday - said they recognised the attacker from a photograph and said he was of middle-eastern or Pakistani origin, had children, and had lived in the area for a number of years.
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Neighbours said he was known locally as “Abz” and identified him as the terrorist wearing an Arsenal shirt in a photo showing him crumpled on the ground after being shot by armed police, the Sun reported.
According to The Times, the Barking suspect, in his 20s, had preached to people at his flat, worked on the transport network and worked for a few hours a week at an Islamic fitness centre where he also took part in boxing and taekwondo.
Housewife Erica Gasparri, 42, told The Times she had reported the suspect to police last year after challenging him in a park near a school.
She said: “They were waiting for the children of the neighbourhood. They would give the children chocolate while talking to them. They would pray in the park for hours.”
A friend told the BBC Asian Network he had reported him to the anti-terror hotline after he began expressing increasingly radical views and justifying terror attacks, but the friend said he was never arrested.
The Daily Mail reported the suspect had featured in the Channel 4 documentary The Jihadis Next Door, which filmed alleged extremists.
Salaudeen Jailabdeen, 40, who lives in a neighbouring block of flats, said the suspect had once been ejected from a local mosque for interrupting an imam.
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And the Telegraph quoted a spokesman for the Jabir Bin Zayd Islamic Centre as saying: “The imam was forced to ask him to leave two years ago.
“He was giving a speech on the up-and-coming general election and the imam was explaining how it was important to vote wisely.
“He got angry, complaining that it was nothing to do with him, and interrupted the imam. He was then asked to leave.”
But in a statement on its website, the mosque said: “We feel until the police release more information it is not appropriate for us to speak about anyone that may or may not have prayed here.”
Neighbours near the Barking flats where he lived said he had been well-known to the community.
Damien Pettit, 31, who said he could not be sure the man pictured was definitely his neighbour, said the man was “very much involved in the area”.
Neighbour Jibril Palomba described how the man he believed he recognised in photos online had once advised him of the need to be a faithful Muslim.
Another neighbour, Ken Chigbo, claimed the attacker, wearing the same Arsenal shirt, had come to ask him about hiring a van hours before the atrocity.
Mr Chigbo, who spoke with the attacker on Saturday, told Sky News: “We were having a general conversation because I am in the process of moving house at the moment.
“I had a big van up here and he came up to me and said, ‘Oh, Ken, you are moving’. He was usually a really nice, friendly guy but this time it was on a different level of nice.
“He was asking me where I am moving to, and then he started asking about the van.
“He said to me, ‘Oh, where did you get your van, Ken? How much is it, is it possible to get in automatic?’ - all these specific questions about the van, which obviously now makes sense in my head.
“At the time I didn’t think anything of it.”
Little is known about the first attacker’s accomplices and addresses have also been raided in East Ham and Newham in connection with the attack.
Irish broadcaster RTE reported authorities found an Irish identity card on the body of one of the suspects, believed to be of Moroccan heritage, indicating he had previously lived in Ireland.