The first name to emerge from the counter-terrorism investigation into the bomb attack on the London Underground last week was that of Yahyah Farroukh.
The 21-year-old was arrested late on Saturday night, more than 36 hours after a device detonated on an eastbound District Line train at Parsons Green station, west London.
He was the second man taken into custody. An 18-year-old was arrested at Dover port in Kent earlier on Saturday, but has not been named.
Since his name was made public, a variety of witnesses, officials, and acquaintances have been speaking out about Farroukh, who has yet to be charged with anything.
Read on to find out what we know about Farroukh so far.
Farroukh is 21 years old. His Facebook lists his date of birth as 28th January, 1996.
He came to the UK from Syria, though it isn't clear when. His Facebook lists his home city as Damascus, the Syrian capital.
Damascus has never come under the control of ISIS, and is the seat of power for Bashar al-Assad's government.
But the city has still been a centre of fighting, and is regularly targeted in bomb attacks.
His Facebook profile says that he went to West Thames College in Isleworth, southwest London.
Farroukh's page says he studied ESOL (English for Speakers of Other Languages), a course meant to give its students a basic grounding in the language.
According to his Facebook, he began at West Thames College in December 2015, when he would have been 19 years old.
A spokeswoman for the college refused to comment when contacted by Business Insider.
Farroukh was raised in the care of a foster couple in Sunbury-on-Thames, Surrey, according to a local politician.
Ian Harvey, a Conservative councillor and the leader of Spelthorpe Borough Council, told the Press Association that it was "widely known" that Farroukh lived with Ronald and Penelope Jones as a foster child.
The couple has fostered more than 300 children over several decades at their home in Sunbury-on-Thames. In 2010 the Queen gave them both MBE awards for their work.
The property was raided on Saturday ahead of Farroukh's arrest, and was surrounded with an imposing metal police cordon while specialist officers investigated.
On Friday, a local resident's CCTV camera captured footage of a man carrying something which resembled the Parsons Green bomb, though it is not clear if it is Farroukh.
According to media reports, Farroukh moved out of Sunbury-on-Thames around a year ago.
The Daily Mirror published a brief interview with neighbours in Stanwell, not far from Sunbury-on-Thames, who said they had lived next door to Farroukh.
They said "I think he moved in about 14 months ago," adding that they think he has family in Scotland.
He worked in a chicken shop in West London.
Farroukh's arrest took place outside Aladdins, a fast food outlet in Hounslow, west London, which specialises in fried chicken.
He was arrested after work on Saturday.
Undercover officers carried out the arrest - which was filmed by witnesses - around 11:50 p.m. on Saturday.
A manager at Aladdins confirmed in a phone call with Business Insider that Farroukh was an employee at the store.
Farroukh appears to have been keen on London's nightlife.
Farroukh's Facebook shows an affinity with London's drinking culture, which may also have been a source of work.
A list of employers (which did not include Aladdins chicken shop) featured Dope Diamond Entertainment and BSQ London, both of which are advertising club nights in Hounslow.
The page does not specify a particular type of work for either company. A photograph of Farroukh appears to show him posing under disco lights with two other men.
He shared occasional posts about the Syria conflict.
Publicly visible posts addressed the conflict, and objected to the British government's decision to extend its bombing campaign against ISIS from Iraq into Syria.
What he shared emphasised human suffering but did not appear to make a political point.
He could spend the next 12 days in custody without being charged.
Farroukh was arrested ten minutes before midnight on Saturday under the Terrorism Act and taken to an unspecified police station in south London.
Police can usually only hold suspects for 24 hours before either charging them or letting them go (they can apply for up to 96 hours for serious crimes).
But in terror investigations, police are allowed to detain people for 14 days, which means that Farroukh could remain behind bars until September 30.
If he is charged with a serious offence he could then be kept in custody until a trial is arranged.