Cops in the London suburb of Hounslow busted 21-year-old Yahyah Farroukh outside a fried chicken shop, according to the Guardian, after police apprehended his 18-year-old accomplice while he was trying to escape the United Kingdom through the port city of Dover.
Images published by the Sun on Sunday night appeared to show Farroukh being arrested by police in Hounslow after a struggle, and officers are understood to have begun searching the chicken shop soon after.
Farroukh used to be cared for by foster pair Ron and Penny Jones, whose house in Sunbury-on-Thames, Surrey, was raided on Saturday. Metropolitan Police officers were still searching the area on Monday morning, the Guardian reported.
The Joneses have been respected foster parents for nearly 40 years and looked after up to 300 children, including eight refugees.
Friday's attack, which saw 30 injured after a crude improvised explosive device in a bucket was left with a timer on a London suburban subway train - a network known as the Tube in the United Kingdom - was detonated during the Friday commuter surge.
Officials said the blast was caused by the partial detonation of a failed bomb, which experts said could have killed everyone in the carriage.
The Islamic State claimed responsibility for the attack.
He said armed police will maintain a strong presence this week.
Witnesses to Farroukh's arrest said they first thought he was getting jumped when police rugby tackled him to the floor.
"One thing I understand is that he (the 18-year-old) was an Iraqi refugee who came here aged 15 and his parents died in Iraq", said Ian Harvey, Leader of Spelthorne Borough Council, which covers the Sunbury area. "I guess because it holds important information".
An apparent Facebook page for Farroukh identified him as a native of Damascus in Syria.
With the arrest of the suspects, the UK Home Secretary Amber Rudd announced that the country's terror treat level, which had been raised to its highest at "critical", would be lowered back to "severe" as "sufficient progress has been made" into the investigation.
Assistant Metropolitan Police Commissioner Mark Rowley said police had gained a "greater understanding" of how the bomb was prepared but said there was "still much more to do".