A grinning student who planted home-made bomb on a busy Jubilee line train told police he had dumped his rucksack "as a prank" when he had time to kill between lessons.
Former altar boy Damon Smith, 20, was found guilty of planting the device – made using a £2 Tesco clock – on the packed Tube train on Wednesday.
The discovery of Smith’s rucksack, packed with explosives and ball bearing shrapnel, on a Tube train in north Greenwich on October 20 last year, sparked chaos on the capital’s transport network.
Disturbing footage, released by Scotland Yard, following a trial at the Old Bailey, shows Smith appear to suppress laughter as he confirms his name and age to officers during a police interview.
When asked to “introduce himself” by a detective, he replies with a smile: “I’m Damon, I live in London and I go to university.”
He then confirms his name as Damon Joseph Smith and gives his date of birth as November 23 1996.
Clad in grey sweatshirt, Smith nods along and continues to smile, as the officer explains why the information is being recorded.
In a second video, Smith describes how he "thought it would be a good idea to leave his bag for a prank" before going to Starbucks.
He said: "As I was on the Tube, I realised It was going to Stratford and I thought it would be a good time to leave my bag for a prank.
"And, then I got off at the station and then I realised I had two hours to kill or something before my next maths lesson. I got on the bus and went to, I think, it's Starbucks or something."
Shocking images have also been released of the weapons-obsessed student posing with a BB gun.
Upon his arrest, the autistic student admitted making the bomb but claimed he only meant it to spew harmless smoke as a Halloween joke.
He told police he had been inspired by watching bomb prank video on YouTube channel Troll Station.
A search of Smith's home in Rotherhithe, south London, revealed his fixation with guns, explosives and other weapons.
Police seized a blank-firing self-loading pistol and a BB gun, both bought legally, as well as a knuckleduster and a knife which he showed off in an online video.
Pictures were also recovered of Smith with guns, including one on a laptop labelled "2016 an Islamic State fighter".
Smith watched YouTube videos on explosions and posted a picture of himself on Facebook in a Guy Fawkes mask holding handcuffs and a knuckleduster, jurors were told.
He professed to be interested in Islam as "more true" than Christianity, but denied being an extremist.
He posed next to an image of the Brussels-born Islamic terrorist alleged to have masterminded the attacks in Paris in November 2015, the court heard.
In his defence, extracts of a psychiatric report were read out in court confirming an autism spectrum disorder.
He had been interested in bomb-making since the age of 10 and said that it was "something to do when he was bored".
Smith denied possession of an explosive substance with intent but admitted the lesser offence of making a bomb hoax.
A jury rejected his explanation and found Smith guilty of the more serious charge after deliberating for two hours.