NBC security analyst Duncan Gardham says Butt, 27, was part of a radical group in East London who support ISIS and had attracted concern from friends and neighbors. Police on Monday said Butt also used the name Rachid Elkhdar.
The group was the subject of a documentary filmed by British TV network Channel 4, in which they were shown in a London park praying to a black flag associated with Islamist groups.
It was as a result of these activities in the park that neighbors Jibril Palomba and Erica Gasparri say they reported Butt to the police.
Gasparri said she confronted him two years ago after she says he had been attempting to indoctrinate her children at a local park.
"The gathering, it didn't look normal. They were talking to the kids about the religion. Kind of like they were imposing themselves. And giving them sweets, and keep them good and playing football with them. At the same time, they were actually, the main talk was about religion. How good it's to be Muslim, to the fact that my kids came home and said 'Mummy, can we become Muslim, there is a gentleman telling us, teaching us.'"
She told Reuters she photographed the men and took the images to local police, "I said: 'These four people I took a picture, they don't look right to me. They look like they are radicalizing the kids. I don't like it.'"
"The police said to me 'You've done a very good thing to come, because this picture, they don't look right. and yes Mrs. Gasparri, you are right.'"
She said local police said they had contacted Scotland Yard and would contact her further but she says she never heard any more from them.
Palomba said his wife reported Butt to authorities after being concerned about what he says his children were being told by him at the local park.
"He was always speaking about Muhammad and religion, Muslim in general, this kind of stuff. And if you are not Muslim, you do not follow in the religion of Muslim you're basically going to hell," he told Reuters.
Gardham says even though the suspect may have been reported to authorities, it can be tough for security services to prioritize who to investigate with the greatest urgency. “The point is they talk about shooting the crocodiles nearest the boat and that's the image that comes up again and again. They have to deal with the big plots with the guys they know are planning things right now and that means they can't always be watching the guys that are perhaps floating around on the edges of these things.”
Another neighbor, Asim Uddin, told NBC News that “most neighbors kept a distance” from Butt.
“He didn’t look very approachable,” Uddin said. “He wasn’t very active — didn’t entertain many gatherings or have a lot of people over. He did play football with the local kids, once in a while.”
At a mosque last Friday, Uddin said, Butt was kicked out after getting in an argument with the imam about politics.
“Once, I got into an argument with him about a parking permit,” Uddin told NBC News. “He wasn’t using one. I asked him to get a permit and follow the law. He told me, ‘I don’t follow the system,’ and walked off.”
Metropolitan Police Commissioner Cressida Dick said she was confident there were only three perpetrators, “We believe there were just three attackers, and we need to work out whether anybody else knew anything or helped at all — and that is what we are doing as we speak. So I don't want to compromise the investigation, I don't want to predict what it will find. But these were the attackers.” Dick said.
Neighbor Ikenna Chigbo said he recognized Butt from images on television which showed him on the ground in the aftermath of the attack wearing the same clothes he'd seen him in earlier in the day.
"God, I couldn't believe it ... He was wearing the same top yesterday," Chigbo told NBC News' British partner ITV News on Sunday. "He had the same shaved head and beard. I really could not believe it."
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