LONDON — A teenager once honored as his school's student of the year went on trial Wednesday, accused of planting a bomb that partially detonated on a crowded London subway train last year.

Iraq-born Ahmed Hassan is accused of making a homemade bomb and leaving it in a subway car hidden in a plastic bucket inside a supermarket bag, injuring 30 people.

The 18-year-old is charged with attempted murder and using the chemical compound TATP to cause an explosion.

Prosecutors said Wednesday there were 93 people in the train car when the bomb partially exploded during the morning rush hour on Sept. 15.

Officials said there would have been many more injuries and probably deaths if the device had fully exploded.

"Had the device fully detonated, it is inevitable that serious injury and significant damage would have been caused within the carriage," prosecutor Alison Morgan said. "Those in close proximity to the device may well have been killed."

Video played for the jury showed an explosion inside the subway car followed by a large fireball that caused many burns and severe injuries.

Hassan had successfully claimed asylum after arriving in Britain in 2015 by traveling through the Channel Tunnel on a truck. He didn't have identity documents.

He was eventually placed in a foster home after telling authorities he feared being persecuted by the Islamic State group in his home country.

Prosecutors said that he won a "student of the year" prize at Brooklands College and used the 20-pound ($28) Amazon voucher that was his prize to purchase hydrogen peroxide, a vital component in the shrapnel-packed bomb.

The attack was one in a series of extremist actions in Britain last year. The country's threat level remains at severe, indicating an attack is considered highly likely.

It was briefly raised to "critical" — meaning an attack was judged to be imminent — after the subway attack when Hassan remained at large.

Hassan has denied the charges.