These are the first pictures of a suspect being held by police investigating the Parsons Green bombing.
Yahyah Farroukh, 21, is listed as living at an address in Stanwell, Surrey, which was searched by officers on Sunday.
He was arrested at a fried chicken shop in Hounslow on Saturday night.
Another 18-year-old was detained at Dover ferry port on Saturday morning.
The younger man is suspected of planting the device, which exploded on a District Line train on Friday morning, injuring 30 people.
Police said the two men are being questioned by police on suspicion of offences under the Terrorism Act.
Both men are believed to have spent time in the care of Penelope and Ronald Jones, who received MBEs for services to children and families in 2010.