A convicted Canadian terrorist affiliated with the 2006 "Toronto 18" plot has been reportedly killed in the Syrian civil war.

Ali Dirie, who turned 30 in August, had pleaded guilty in 2009 to smuggling a handgun across the Canada-U.S. border for a terrorist group.

Records show his sentencing, part of a landmark Canadian prosecution, was watched closely at the time by U.S. diplomats, who cabled Washington with a dispatch titled: "Light sentences continue for Toronto convictions."

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CBC reported news of Mr. Dirie's death Wednesday night. A source independently confirmed it to The Globe and Mail. News of his death raises questions about whether the Canadian criminal justice system is doing enough to rehabilitate or monitor convicted terrorists.

Released from prison just two years ago, after completing his sentence, Mr. Dirie again became a topic of conversation around Toronto mosques in recent days, as rumours spread that he had been killed overseas in the Syrian war.

The word was that "Ali Dirie has been martyred," said Mubin Shaikh, a Toronto man who years ago worked for police as an undercover mole against the wider group.

Mr. Shaikh, who said that Mr. Dirie's family members spread the news, argues that government officials must do a better job of "deradicalizing" convicted terrorists. "We got to have something. We can't afford to do nothing," Mr. Shaikh said. "They're out, they're back and nothing is in place."

The war in Syria has proven to be a magnet for young radicals intent on the armed overthrow of the regime of Bashar al-Assad. Some fighting factions, such as the Al-Nusra Front, comprise Sunni fundamentalists who consider the conflict a holy war.

It is not clear where Mr. Dirie may have died, or whether he was affiliated with a specific faction. But he is reported to have been fighting alongside the rebels.

Eight years ago, Mr. Dirie was in league with a group of young extremists in Toronto in their teens and 20s. After he was caught smuggling a handgun across the Canada-U.S. border in 2005, members of the wider group went on to organize terrorist training camps and plot the bombings of government targets.

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Mr. Dirie's arrest led to a much wider investigation. Police arrested 18 suspects in June, 2006, and eventually convicted 11 of them on terrorist offences. In 2009, Mr. Dirie pleaded guilty to having smuggled the gun on behalf of the wider terrorist group.

Before his jail term finished in 2011, the Parole Board of Canada ruled that Mr. Dirie had "no remorse, empathy or concern for the innocent people who were to be targeted by the terrorist attacks/plans."

While Mr. Dirie had received a nominal seven-year sentence, he was also given two-for-one credit for the 30 months he spent jailed awaiting trial. (Such "dead time" considerations were standard in the Canadian correctional system at the time.)

According to CBC News, Mr. Dirie entered Syria with a passport that was not his own.

Mr. Shaikh, the former mole who had once infiltrated the Toronto 18 cell, recently helped organize an outreach event that introduced Muslim children to RCMP officers. He said Canada has to do more work to keep extremists from recidivism.

"You're dealing with an ideology here," he said. "You think you can enforce it into nonexistence?"