The teenager was arrested in connection with the Parsons Green attack was reportedly in trouble with police before, according to neighbours of the couple who fostered him.
Serena Barber, 47, who lives in a property backing on to Richard said Penelope Jones' house in Sunbury-on-Thames told The Mirror, "All I know is that they have two boys at the moment, both are foreign. One is very quiet and polite, the other who is 18 is awful."
Another, who gave his name as Richard, added: "One of the men living there was a real troublemaker."
He added: "Most of the street had complained about him at some point in the past few months. "He was in trouble with the police a few times."
He said that they had heard the 18-year-old suspect was arrested near Parsons Green, where the attack took place.
Penelope, 71, and her husband Ronald, 89, who fostered the 18-year-old are lovely, he said, adding that it often seemed some of the people they took in were taking advantage of them.
"As far as I'm aware, he didn't work or anything, he just sponged off them. I imagine they will have been very shocked by the police today, Ronald in particular is nearly 90 - he's a frail man. You have to feel sorry for them."
In 2010, the couple were given MBEs for their services to children and families. They have fostered more than 250 children, according to community group Elmbridge CAN.
The 18-year-old was arrested in Dover on Saturday morning, where he was allegedly trying to leave the country. He remains in custody.
