The man accused of the Parsons Green Tube bombing blamed Britain and America for the deaths of his parents in Iraq, the Old Bailey has heard.
College lecturer Katie Cable said Ahmed Hassan told her it was “his duty to hate Britain” because of what happened to his family.
The court also heard he believed his father had been killed by US bombing.
Mr Hassan, 18, denies attempted murder and causing an explosion likely to endanger life.
He allegedly packed a bucket with 400g (14oz) of TATP explosives and shrapnel and left it on the District Line train on 15 September 2017.
It partially exploded causing a fireball to rip through a carriage during the morning rush hour, the Old Bailey has heard.
Barnardo’s worker Youseff Habibi got to know Mr Hassan when he was living in a children’s home in Surrey.
Asked about the defendant’s background, Mr Habibi told jurors: “His father was a taxi driver and one morning he went to work and a bomb fell on him and he died.
“And his mum died when he was much younger. He said ‘I don’t remember my mum.'”
Prosecutor Alison Morgan asked: “Did Mr Hassan ever say who he blamed for that?”
Mr Habibi replied: “America. He said it was American soldiers and American army bombing.”
The witness also said he once found Mr Hassan listening to an Arabic song on YouTube along the lines of “coming to the slaughter in your own home”.
Also giving evidence on Monday, Ms Cable, a lecturer and mentor at Brooklands College in Weybridge, said she recalled Mr Hassan telling her “his father was blown up and his mother had been shot”.
She said he talked about Tony Blair and events in Iraq, adding: “I believe the anger was very clear. He referred to being angry several times.”
Ms Cable recalled an occasion in August 2016 when she saw a What’s App message on his phone which said: “IS has accepted your donation.”
On the same occasion, he allegedly told her: “It’s my duty to hate Britain.”
The court also heard how, in January 2016, the accused met Home Office immigration officials.
Barnardo’s worker Zoe Spencer, who accompanied Mr Hassan, then aged 16, said he told he was “forced” to train “how to kill people” for three months by the Islamic State group.
He told them he escaped when Iraqi soldiers came into IS territory and told everyone to go, she said, but he denied he had been sent to Europe to work for the terror group.
Days after the interview, Ms Spencer told the court she saw Mr Hassan looking at a picture of people in balaclavas with guns and the black flag of IS.
The trial continues.