Yahyah Farroukh, 21, was arrested in Hounslow, west London on Saturday night after he finished his shift at a fried chicken shop.
Both Farroukh and an 18-year-old man, understood to be the suspected bomber, are being questioned by counter terrorism officers following the incident at Parsons Green tube station on Friday morning.
Thirty people were injured after a homemade bomb partially exploded in a underground train carriage.
Both men are believed to have spent time in foster care with Penelope and Ronald Jones, aged 71 and 88 respectively, who previously received MBEs for services to children and families.
• READ MORE: Edinburgh venues up security after Parsons Green attack
According to his Facebook profile, Farroukh is originally from Damascus and is living in London, having studied English at West Thames College.
However neighbours said Farroukh has family in Scotland, with relatives living in Aberdeen or Edinburgh.
In comments reported yesterday, Pat Hodge, 59, said: “My wife and I have sat outside in the communal garden with him in the summer and had ice lollies. He seems like a nice chap. Sometimes his family come down from Edinburgh, I think it’s his brother and two nephews. They’re all really lovely to talk to.
“They’re obviously Arabic but the kids speak with perfect Scottish accents. Sometimes he and his friends go out in the garden with their prayer mats and shisha pipes.”
Suleman Sarwar, 43, who owns Aladdin’s Fried Chicken on Kingsley Road, Hounslow, with his brothers, said Farroukh worked at the takeaway.
Mr Sarwar said: “Yes he is familiar. I recognise him as a member of staff.
“He was very normal. I don’t know how long he worked here. It was surprising seeing him on the news.”
Mr Sarwar added that Farroukh had been working on Saturday and was arrested outside the shop after his shift at around 11.30pm.
He said: “It was at that point that the police all grabbed him.”
• READ MORE: Parsons Green: Bomb suspect arrested at port of Dover
The younger suspect was detained on Saturday morning in the departure area of Dover ferry port, which is the busiest ferry hub in Europe and a gateway to the French coast.
Both men remain in custody for questioning over the attack.
Meanwhile, new CCTV footage appears to show a suspect on his way to plant the tube bomb at around 7am on Friday morning.
The shows a figure dressed in grey carrying a distinctive white Lidl carrier bag.
The device which went off at Parsons Green appeared to be inside a bucket within the same type of bag.
The footage was obtained from a camera outside Ecco La Vera pizzeria on Vicarage Road in Sunbury-on-Thames.