Damon Smith, a former altar boy, has been jailed for 15 years for planting a homemade bomb on a

Weapons-obsessed Damon Smith built the device at home with a clock from a supermarket after finding an online al-Qaeda article titled “Make a Bomb in the Kitchen of Your Mom”.

Smith, 20, claimed it was a Halloween prank but was found guilty of possession of an explosive substance with intent following a trial at the Old Bailey.

Smith left the bomb on the floor of a busy Tube train. Picture: Facunda Arrizabalaga/EPASource:AAP

The defendant, who has autistic spectrum disorder, smiled in the dock as Judge Richard Marks QC sentenced him to 15 years in a young offenders’ institution. The judge said on Friday that although Smith had an interest in Islam, he was not motivated by terrorism.

But he told the defendant: “Whatever the position, the seriousness of what you did cannot be overstated, not least against the background of the fear in which we all live from the use of bombs here and around the world, an all too timely reminder of which were the events in Manchester earlier this week.”

Smith’s lawyer, Richard Carey-Hughes QC, said Smith was “sorry” for the fear and disturbance he had caused and had “learned his lesson”.

Passengers spotted Smith’s abandoned rucksack on the Tube train. Picture: APSource:Supplied

The trial heard Smith packed a rucksack with explosives and ball bearings on the morning of October 20, 2016.

The college student was caught on CCTV flicking through a textbook before getting off the train and leaving the bomb on the floor, timed to go off within minutes.

Passengers spotted the abandoned rucksack and alerted the driver, who at first dismissed it as lost property and took it into his cab, jurors were told. During the journey, he spotted wires coming out of the bag and raised the alarm as he pulled into the station.