Iraqi teenager Ahmed Hassan was taken into foster care and interviewed by authorities in 2016 and claimed he had not been sent by the terrorist group to launch an attack.
He denies building a homemade bomb that partially exploded on the London Underground in September last year, and attempting to kill commuters in the height of morning rush-hour.
The Old Bailey heard that the 18-year-old bought the necessary chemicals online using a £20 Amazon voucher awarded for being named “student of the year” at Brooklands College in Surrey.
Mr Hassan allegedly seized a “window of opportunity” to prepare the device while his foster parents were on holiday in early September last year.
While the elderly couple, who were made MBEs for their decades of service to children, were away he allegedly researched explosives, ordered the ingredients online and collected them from a friend’s home.
Mr Hassan was placed with the couple after arriving in Britain in the back of a lorry via the Channel Tunnel in October 2015.
He had no identity documents, but gave his full name as Ahmed Hassan Mohammed Ali to Home Office officials who interviewed him the following January at Lunar House in Croydon.
Mr Hassan told them he was claiming asylum in Britain as he was “in fear of Isis as a result of what had happened to him in Iraq”, the court heard.
He told officials he had been “trained to kill” by the terrorist group and indoctrinated in “what Allah believed was right”.
The teenager denied he had come to Europe on their behalf and said militants “forced” him to go with them as they advanced through Iraq and threatened to kill his family if he refused.
Mr Hassan described training alongside around 1,000 people and said he only escaped after the territory was retaken by Iraqi government forces, who told the children to flee.
Months after the interview, a Barnado’s staff member who spoke Arabic allegedly caught him listening to an Islamic nasheed [song], with words to the effect of: “We are coming with you to the slaughter in your home/country.”
One of his supervisors also allegedly saw Mr Hassan watching what appeared to be an Isis propaganda video video of people in a truck wearing balaclavas, holding machine guns and the group’s flag.
In April 2016, the teenager was referred by Surrey social services to Brooklands College where he was given a mentor who helped him find his foster home in Cavendish Road, Sunbury, in Surrey.
At the time Mr Hassan allegedly set about causing carnage on the Tube at Parsons Green, his asylum claim was still outstanding.
The jury was told that the day before the attack on 15 September, Mr Hassan set off bought metal items for shrapnel from Asda and Aldi in Feltham, west London.
The device he allegedly created contained Isis’ signature explosive TATP [triacetone triperoxide] and 2.2kg of sockets, screws, bolts, nails, knives, screwdrivers and other shrapnel aimed to cause “maximum harm and carnage”.
Prosecutors said Mr Hassan put the device inside a white bucket, with an improvised detonator and timer, inside a Lidl bag.
The defendant allegedly left his home shortly before 7am and took the overground train from Sunbury to Wimbledon, passing schoolchildren and commuters on his way to the District Line interchange.
In a toilet in Wimbledon station, he set the timer and boarded the Tube before getting off at Putney Bridge, one stop before Parsons Green, jurors heard.
Prosecutor Alison Morgan: “At any point, should he have wanted to, he could have stopped the timer. He could have pulled the wires out of the device. He could have stopped the detonation.
"The CCTV footage from inside the carriage shows that at no stage did the defendant reach inside the bag to do anything."
There were 93 people in the packed Tube carriage when the device partially exploded in at 8.20am, sending a fireball into the air and severely burning commuters.
One passenger, Jelena Semenjuk, said she noticed a bag on the floor and a man fitting Mr Hassan’s before she heard a ”loud bang“ and noticed her coat was on fire.
She suffered burns to her legs, hands, and face, causing her eyebrows and lashes to be singed off, the court heard.
Aimee Colville saw "shards of glass flying through the air and then flames" and "smell herself burning and saw her hair was on fire".
Stephen Nash noticed a ”blinding light and the feeling that he was in a furnace engulfed in flames“, the court was told.
An expert concluded it was ”a matter of luck“ that the bomb did not fully explode, saying the initiator could have come loose or the device may not have been well constructed.
As the bucket continued to burn, hundreds of passengers fled the train and several were injured in the crush to escape Parsons Green station up a single staircase.
The court heard that after “calmly” walking away from Putney Bridge station, Mr Hassan boarded a bus where he was caught on CCTV removing the SD card from his phone and chewing it to destroy it.
He then boarded a train to Richmond and onwards to Brighton, changing clothes several time to switch from a grey jumper, to maroon one, to a Chelsea shirt bought alongside other supplies in Ashford.
The jury heard Mr Hassan arrived in Dover at around 2.30pm, and bought a new mobile phone that he used to read BBC news coverage of his own bombing.
When he was arrested at the Kent port, he had £2,320 in cash and told police he was responsible for the device, the court was told.
Investigators recovered the destroyed SD card from Mr Hassan’s phone but said there was no record of how the bomb was built because the Mac laptop social services gave him for his studies had been completely wiped the day before the attack.
Mr Hassan denies attempted murder and using the chemical compound TATP to cause an explosion that was likely to endanger life.
Additional reporting by PA