The foster parents of the Parsons Green Tube bomber say they feel "betrayed" by his actions - and claim they were never warned that he had admitted being "trained to kill" by militants shortly after he arrived in Britain.
Ron and Penny Jones took Iraqi asylum seeker Ahmed Hassan into their home in Surrey, and said he "seemed like the loveliest boy we could have asked for".
But unbeknown to them, the teenager was plotting to cause carnage in central London, secretly making 400g of "Mother of Satan" explosives while the couple were away and packing the device with 2.2kg of screwdrivers, knives, nuts and bolts.
On Friday he was convicted of attempted murder after the bomb partially exploded on the floor of a Tube carriage at Parsons Green, injuring 51 passengers.
During his trial, the Old Bailey heard he had wanted to avenge the death of his father in Iraq and was "disappointed" when the bomb only partly detonated in a huge fireball.
It was also revealed that the 18-year-old had already come to the attention of the Home Office, telling officials in January 2016 that he was recruited by IS and forced to train with them.
During an immigration interview at Lunar House in Croydon, he said: "They trained us how to kill. It was all religious based."
In an interview with the Daily Mail, Mr and Mrs Jones said the authorities "should have been honest" with them, and spoke of their disbelief at how events unfolded.
"He still needed somewhere to live, he still needed to be looked after, but I would have liked to have known because we could've been looking out for signs of radicalisation," said Mrs Jones.
Mr Jones, 89, added: "If we'd known, we could have been more watchful. I still can't believe he did it. He seemed like such a good kid."
Hassan, who arrived in Britain on the back of a lorry in 2015, was referred by Barnardo's and Surrey social services to the anti-terrorism Prevent scheme, but kept his murderous plans a secret.
A review of Hassan's dealings with Prevent is under way to see whether any lessons can be learned.
Mr Jones, who was awarded an MBE in 2010 along with his wife for services to fostering, told the Mail he had been "blaming myself but I've had nothing to be suspicious of".
Mrs Jones added: "I can only say he betrayed me. And out of the 269 kids we've had, he's the only one I can say that about."
Surrey County Council told the Mail: "We're sorry Mr and Mrs Jones feel we didn't support them well enough but we told them about Hassan's background at the time he was placed with them."
The authority added it placed a "high value on openness with all our foster carers" to keep them informed about any risks, adding: "This was our approach with Mr and Mrs Jones and our social workers also gave them regular updates.
"Supporting Mr and Mrs Jones continues to be a priority for us."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Metropolitan Police / PA Wire.