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.
Mr Hassan allegedly seized a "window of opportunity" to prepare the device while his foster parents were on holiday in early September previous year.
The Iraqi asylum seeker, who had told immigration authorities that Islamic State trained him to kill, allegedly assembled the device while his foster parents in Sunbury-on-Thames in Surrey were visiting Blackpool, and allegedly packed it with shrapnel to cause maximum carnage, buying metal items from Asda and Aldi.
Hassan denies attempted murder and causing an explosion likely to endanger life or property. They were fortunate. Had the device fully detonated it is inevitable that serious injury and significant damage would have been caused within the carriage.
Hassan claimed asylum when he arrived in Britain on the back of a truck travelling through the Channel Tunnel from France, saying he was in fear of Islamic State.
After planting the bomb, the jury was told the suspect then "calmly" got off the train further down the line and boarded a bus that followed the route of the Tube towards Parsons Green station.
Hassan is then alleged to have left the Tube train one stop earlier at Putney Bridge, having left the Lidl bag behind.
He denied he had been sent to Europe to work for IS, the court heard.
A London evening newspaper poster outside Paddington tube station in London, after a terrorist incident was declared at Parsons Green in September.
On September 15, he left his home shortly before 7am and took the train from Sunbury to Wimbledon, carrying his bomb past schoolchildren and commuters, jurors heard. He could have stopped the detonation.
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Video played for the jury showed an explosion inside the subway auto followed by a large fireball that caused many burns and severe injuries.
"The CCTV footage from inside the carriage shows that at no stage did the defendant reach inside the bag to do anything".
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.
"The prosecution therefore alleges that the defendant intended that this should be a lethal attack".
Officials said there would have been many more injuries and probably deaths if the device had fully exploded.
The initiator could have come loose when it was transported or the device may not have been well constructed, the court heard.
Stephen Nash noticed a "blinding light and the feeling that he was in a furnace engulfed in flames", the court was told.
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.
Alison Morgan, prosecuting, told the Old Bailey that Hassan had bought five litres of hydrogen peroxide.