A special CBC News investigation has uncovered the identity of a third member of a group of former London, Ont., high school friends now at the centre of a horrifying tale of young Canadians getting mixed up with al-Qaeda and international militants.

CBC News has learned that Aaron Yoon, now about 24, is likely the only survivor among this perverse band of brothers, two of whom died while staging a bloody attack on an Algerian oil refinery three months ago.

International intelligence sources say Yoon, a Canadian of Korean descent, flew to North Africa with three others, but wound up in jail before the al-Qaeda attack in January that killed 37 refinery workers in Algeria.

Two of Yoon’s former London schoolmates, Xris Katsiroubas and Ali Medlej, were among several dozen al-Qaeda-linked militants involved in the attack.

Sources say the two probably blew themselves up at the end of the four-day siege, but only one could  be identified through DNA tests.

There is no evidence Yoon ever intended to participate in the attack, even if he had not been incarcerated, and his brother says Aaron has had no contact with the others in over a year.

A fourth member of the London group appears to have disappeared.

All of this apparently came as a shock to Yoon’s family still living in London.  

Yoon’s brother, reached by CBC News at the family home, said he had no idea Aaron had been jailed, and in fact spoke to him by phone a few weeks ago.

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International intelligence sources say Aaron Yoon, a Canadian of Korean descent, flew to North Africa with three others, but wound up in jail before the al-Qaeda attack in January that killed 37 refinery workers in Algeria. (CBC)

At the time, Yoon seemed free to travel, the brother said.

It is still a mystery exactly how a Korean-Canadian high school kid wound up in league with classmates bound for death in a faraway desert.

Yoon grew up on the third floor of a three-storey apartment  building.

Like the others in the ill-fated brotherhood, he went to London South Secondary School where, acquaintances say, he was a good student.

He was raised a Catholic.

A year before his graduation, however, Yoon converted to Islam like his pal Katsiroubas, and together with Medlej, they were given space in the school to perform their prayers and other rituals of their new faith.

Not long after he left school, he also left home and moved in with Medlej.

Yoon appears to have been on the radar of police and intelligence agencies in Canada.

In June of last year, barely six months before the attack on the Algeria refinery, RCMP were in London asking questions about Yoon and his two chums, Katsiroubas and Medlej.

Ahmed Elturk, who runs programs for Muslim youth in London, recalls being interviewed by the RCMP who were most interested in the whereabouts of Medlej.

"They were trying to find information if I had an idea where he would be, or if I knew anyone who had an idea where he might be," Elturk told CBC News.

 He recalls the RCMP officer showing him photographs of Medlej and a Korean-Canadian.

The Department of Foreign Affairs, asked to comment on whether Yoon, a Canadian citizen, is being held in a foreign jail, replied, "we can't comment on national security matters."

Canada's record 'sound'

On Tuesday, Immigration Minister Jason Kenney said Canada isn't losing the battle against homegrown extremism.

Speaking in Vancouver, he said he couldn't comment directly on the cases because the RCMP are still investigating, but when he was asked if he was worried Canada was losing the battle he said, "No, absolutely not."

"I think actually our record is very sound on this," he said. "We have seen violence in many western European countries and in the United States being inflicted by people who were radicalized in those countries, many of them born and raised in those Western countries."

Kenney says Canadians should be "vigilant," noting that Canada is not immune to domestic radicalization, but said Canadians should also be grateful they haven't faced the kind of violent attacks born out of homegrown radicalization that some European countries have.

"There are a lot of incidents that don't make it to the news where the RCMP and CSIS are preventing or identifying problems before they get too serious," Kenney said.

"And frequently, for example, when information is obtained about perhaps a young Canadian who is on the path towards radicalization, often there's an intervention. Often the police will go and visit his family or perhaps his spiritual leader, and say, this young person is going in the wrong direction. There's an effort to make an early intervention."

Government 'deeply' concerned

Foreign Affairs Minister John Baird said Tuesday that the government wants to recommit itself to dealing with "the challenge of radicalization."

Baird would make no direct comment on the case Tuesday, but said the broad subject is something that "deeply concerns us."

"Canada is far from the only country that has had to deal with this challenge of radicalization," Baird said on a teleconference call from Abu Dhabi following visits to Jordan and Iraq.

"I can say that our intelligence service and the RCMP have worked closely with Algerian officials. I think it goes without saying that we all want to recommit ourselves to do more to combat this real challenge as many countries in the West have."

Pressed for more details, Baird said: "It would probably be best for me to talk to my cabinet colleagues rather than speculate in the media and give my off-the-cuff suggestions while I'm travelling on the road."

Public Safety Minister Vic Toews' office referred all calls to the RCMP. A spokesman for the Mounties would say only that the "investigation into this matter continues and no further information will be given at this time."

Last month, the Mounties first said a Canadian was among those killed in the attack, but wouldn't say if the remains were discovered among the militants or the hostages.

Police later said there was a second Canadian among the bodies of the accused attackers.

Recruitment of Canadians 'quite typical'

The story of the young men should not be viewed as all that unusual for Canada, according to a former assistant director of the Canadian spy agency, CSIS.

Ray Boisvert told CBC News that Canadians shouldn't see the case as atypical.

"Sometimes Canadians see these sort of religious-political motivations as being something that affects others, or just a small part of the community," he said.

"But that's not the case. This is not about Canadians or a particular group. It's about vulnerable youth, falling prey to a nasty subset of religious ideology driven through al-Qaeda narrative, being driven by a sense of adventure, a sense of purpose, a sense of meaning in their life, or perhaps following someone of influence in their life that will lead them to a path of violence."

Boisvert said these "influencers" in somebody's family life will try to "hide in the shadows."

Motivation for the young men's involvement is unclear, say those close to the investigation.

"They do seem sure that this was a perverse type of band-of-brothers pact, that these young men decided to travel together and act together," CBC's Adrienne Arsenault reported.

"Either CSIS decided that these two young men were not a threat, or they lost sight of them. There are a lot more questions to answer," she said.