Evidence leads investigators unraveling London subway plot to foster home An 18-year old man who lived in a foster home has been arrested.

 -- Police in London are focused on a very unlikely location for a suspected bomb factory in the London suburb of Sunbury-on-Thames in connection with the subway attack that sent at least 30 people to the hospital on Friday morning.

The home is owned by an elderly couple, Penelope and Ronald Jones, who were honored by the Queen for serving as foster parents for young men, including some from Iraq and Syria.

An 18-year old man who lived in the foster home has been arrested as surveillance footage made public overnight appears to show a young man leaving the foster house just 90 minutes before the attack carrying a white bag police believe may have contained the bomb used in the attack.

Neighbors were stunned that a foster child might take advantage of the goodness of the elderly couple.

“He was a lovely young man,” Tabitha Jenkins said. “You wouldn’t suspect anything from him. He was polite, courteous to the old couple. They wouldn’t know anything about him.”

On Sunday, a second young man, 21, was arrested nearby, identified in a video by a British tabloid as Yahya Faroukh, a displaced Syrian who lived in London, though his family is spread throughout Europe and Egypt as they await resettlement.

Members of Yahya’s family confirmed to ABC News that the man in the video was Yahya but said they had not yet been contacted by authorities about his arrest.

Yahya is one of nine siblings, and members of his family told ABC News that Yahya never had radical or violent tendencies and the family last spoke with him on Saturday morning and "everything seemed fine and normal and Yahya told them about school and was even talking about getting married."

The family was still mourning the recent and sudden death of their father, however, which Yahya’s brother says affected Yahya especially hard because it happened while he was away.

The second arrest led to another series of police raids at a home disturbingly close to Heathrow Airport.

“The police have made good progress with is an ongoing operation,” said Amber Rudd, Britain’s Home Secretary.

Officials say the forensic evidence raises new questions about the attack, such as whether the bucket bomb used in the attack was a type of explosive designed to release deadly chemicals.

The absence of any metal that could turn into shrapnel suggests to bomb experts that the goal instead was to achieve a release of deadly chemicals.

The threat level has been dropped from critical to severe, but given the series of four attacks in the last six months, British Prime Minister Theresa May told ABC News she wants a hard look at what is being done to prevent them.

“It is necessary for us to look, as we are doing, at whether our police and security service have the full capabilities, the powers that they need,” May said.

ABC News’ Sohel Uddin, Mike Trew, James Gordon Meek, Rhonda Schwartz and Pete Madden contributed to this report.