On Thursday (April 27), 19-year-old Haroon Syed, from Hounslow, pleaded guilty at the Old Bailey to a charge of preparation of terrorist acts between April and September last year, following a failed attempt to get his case thrown out.
The sentence was adjourned until June 8 by judge, Michael Topolski QC, to allow time for a probation and psychiatric report to be done.
The judge said Syed faces a "discretionary life sentence".
The court heard how Syed tried to get weapons online, including a bomb vest or explosives, and searched the internet for busy areas in the capital to launch an attack.
He was arrested by police on September 8 last year, and when asked to provide a password to unlock the device, Syed said: "Yeah I.S.I.S - you like that?"
Last June, his older brother Nadir Syed, also from Hounslow, was jailed for life for plotting an Islamic State-inspired attack on Remembrance Sunday in 2014.
British Security Service officers posing as extremists caught Syed out when he was talking to them online about sourcing the weapons.
At a previous hearing, the court were told of how Syed asked for "gear" for his "opp", to a fake contact, Abu Yusuf on social media and via mobile phone.
When asked to provide details, he said he needed a machine gun and explosive vest, "so after some damage with machine gun do martyrdom ... that's what I'm planning to do."
Syed then met up with an officer, pretending to be Abu Yusuf, at a coffee shop in Slough, where their conversation was recorded.
Despite confessing he had never used a gun before, Syed's conversations with Abu Yusuf continued throughout August, discussing acquiring a gun and making or getting a bomb.
"I might put the bomb in the train and then I'm going to jump out so the bomb explodes on the train ... So ask the brother if he can make that type of bomb with button," he said on August 30, stressing that he needed a portable device.
They arranged to pick up the bomb for £150 the week after.
Syed searched the web for IS, past terrorist attacks, and potential locations to carry out his attack, including an Elton John concert in Hyde Park on September 11 last year.
He asked Abu Yusuf to ensure there were lots of nails in the bomb and added: "I was thinking of Oxford Street ... If I go to prison, I go to prison.
"If I die, I die, you understand."
In legal papers prepared for his defence, Syed was described as "highly vulnerable due to family history, lack of education, addiction to violent online games and the arrest and imprisonment of his brother."
According to his defence, he was groomed by radicals online but he never intended to carry out an attack.
His lawyer Mark Summers QC argued he should have been given help by the Prevent de-radicalisation group rather than steered in the opposite direction.
He said: "The proper response of the State should have been to engage Prevent to help this young man, to steer him away from the path it was feared he was going down, rather than guiding him down it."
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