An impulsive act of rage has led to a decade-long prison sentence for an arsonist whose destructive actions claimed the life of a teenager attending a sleepover.

The tragedy unfolded amid a contentious neighborhood conflict in the heart of Waterloo, where Gregory John Walker hurled a Molotov cocktail into a kitchen, igniting the chaos.

One victim had to leap from a window, suffering severe burns on up to 65 percent of his body as he landed amidst the flames.

The court heard that the 58-year-old displayed a shocking indifference to the gravity of his actions following the blaze.

When a neighbor accused him of starting the fire, saying, “I know you’ve done it,” Walker, then 30, ominously responded, “If you think that was a big fire, wait until you see my next one.”

But Walker had since shown remorse, Justice Dhanji said.

In 2014, as police tried to mount a case against him, he told a witness he “wouldn’t have gone through with it” if he knew children were inside the home.

But evidence showed the former boxer had effectively turned his life around since his deadly actions in 1998, even establishing a not-for-profit for young people.

“There is an element of him attempting to make good on his past wrongs,” Justice Dhanji said.

That was despite Arthur’s family’s obvious desire and lengthy wait for answers.

“While the ledger cannot be squared by the good done by the offender in recent times, that contribution must be taken into account and given weight,” Justice Dhanji said.

With time served, Walker will be eligible for parole in February 2029.

Arthur’s mother Julie Szabo, who ensured the public never forgot her son during repeated media appearances seeking answers, was surrounded by loved ones as the sentence was delivered.

She previously detailed the heavy guilt she has carried since allowing Arthur to have his first sleepover with friends.

“It was going to be the first night he had not slept under the same roof as me,” Szabo wrote in a statement earlier read out in court.

“I said ‘yes’ … I think about that decision a lot.

“I gave him the biggest hug, we both said we loved each other, I didn’t know at the time it would be one of our last hugs.”

“No sentence I impose can right the wrong that has been done,” he said.

Justice Dhanji also took into account a charge of maliciously inflicting grievous bodily harm that Walker committed when he punched a neighbour and bit off part of his ear in April 1998.