Some 93 passengers scrambled to get off the District Line train after a wall of flames engulfed their carriage during rush hour on September 15 a year ago, with witnesses describing a fireball melting clothes, singeing hair, and causing bad burns.
Ahmed Hassan, 18, denied he was sent to Europe to work for the jihadist group but said they took him by force and "they trained us on how to kill", before Iraqi soldiers freed him, according to details revealed at the start of his trial.
Eighteen-year-old Ahmed Hassan is on trial for attempted murder and causing an explosion likely to endanger life.
She said: "Had the device fully detonated it is inevitable that serious injury and significant damage would have been caused within the carriage".
Hassan arrived in Britain in the back of a lorry via the Channel Tunnel in October 2015.
The man accused of planting the Parsons Green bomb boarded a bus towards the station as passengers fled in panic after he left the explosives on a packed Tube train, a court has heard.
There were 93 people in the carriage where the bomb was planted during the morning rush hour in September previous year, the court has heard.
Hassan, of Cavendish Road, Sunbury, Surrey, is said to have used Amazon and Asda to research and buy ingredients for an improvised explosive device (IED) that partially exploded injuring 30 commuters.
Hassan set a crude timing device and got off the train at Putney Bridge station, the stop before Parsons Green.
Jurors were told that while in the care of Barnados, a member of staff who spoke Arabic caught him listening to a "call to arms" song with lyrics along the lines of: "We are coming with you to the slaughter.in your home/country".
Opening the trial, prosecutor Alison Morgan told the jury that just before 8.20am on September 15, an IED partially detonated on a district line shortly after it arrived at Parsons Green Station.
The jury saw images of Ahmed Hassan at Wimbledon Station
Video played for the jury showed an explosion inside the subway vehicle followed by a large fireball that caused many burns and severe injuries. He could have stopped the detonation.
CCTV footage from close to Hassan's home in Sunbury on the day of the attack appeared to show him leaving through the back garden at around 7am, carrying a Lidl bag.
She told the jury she heard a bang, and then people screaming.
Miss S said she suffered severe burns on her legs, as well as burns on her hands and face, and was still being treated six months after the explosion.
Aimee Colville saw "shards of glass flying through the air and then flames".
An expert concluded it was "a matter of luck" that the bomb did not fully explode.
One woman said she could smell herself burning and could see that 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.
Mr Hassan was arrested at the port of Dover the day after the explosion.
They included the initiator coming loose when it was transported or poor construction, the court heard.
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