The 22-year-old Canadian man implicated in the deadly attack on an Algerian gas plant in January threatened to kill one foreign hostage every hour if his militant group's demands were not met.

In exclusive interviews with CBC News, several of his former hostages at the In Amenas gas plant confirmed meeting London, Ont. native Xristos Katsiroubas – a recent convert to an extremist form of Islam – during the attack.

In those interviews — for some, the first public comments on the ordeal since it ended — survivors shed new light on Katsiroubas the militant, painting a picture at odds with the high school photo that has dominated news coverage.

Katsiroubas, who is of Greek-Canadian extraction, apparently wore a beard and fatigues, was constantly carrying what appeared to be an AK-47, and could understand and speak some Arabic.

More significantly, he helped handle weaponry and assemble improvised bombs, said one of the survivors of the ordeal who had a chance to observe him for hours.

Katsiroubas also appeared to play the role of negotiator on behalf of the group of approximately 30 al-Qaeda-like militants who stormed the plant in Algeria near the border with Libya, and held some 800 oil workers hostage. The standoff lasted four days.

Exclusive on The National Tonight and only on The National, we give you a virtual tour of that Algerian gas plant and hear stunning, detailed accounts of what one of the Canadian militants did, according to hostages held by him who lived to tell their stories.

The former hostages all recognized Katsiroubas from the media coverage, and also from a photo shown to them during interviews.

From the start, he stood out among the well-armed militants in the bold morning attack.

"He had eyeglasses, same as John Lennon, and he was skinny, and a small beard then. He speak fluent English," Joseph (Jojo) Balmaceda, a senior instrument technician from the Philippines, told CBC News.

The "blond man" as Balmaceda called him, also "can understand their [Arabic] language."

Just a 'bluff'?

When he came face to face with Balmaceda, Katsiroubas demanded to know his nationality.

Balmaceda was tied up by the militants and remained in close proximity to Katsiroubas at the living quarters for much of his harrowing two days in captivity.

"I heard [Katsiroubas] on the phone: 'If you will not follow our demands … we will start to kill the hostages here every one hour.'"

Joseph Balmaceda, from the Philippines, was a senior instrument technician at the In Amenas facility near the Algerian border with Libya. He was the only hostage to survive an explosion in the truck he was being transported in (CBC)

One of the demands, says Balmaceda, was the withdrawal of the Algerian troops that had surrounded the plant.

For effect, while Katsiroubas was on the phone, one of the other militants would unleash a few rounds into the ground.

Katsiroubas once assured a terrified Balmaceda that it was just a "bluff."

But in reality dozens of foreign workers would ultimately die at the hands of the militants in a bloodbath unleashed by suicide explosions or point-blank shootings.

Others died while being used by the militants as human shields, caught in the crossfire when Algerian forces mounted an assault to end the crisis on its second day.

The attackers belonged to "The Signatories in Blood Brigade," led by Mokhtar Belmokhtar, a well-known Algerian militant and a former senior member of the al-Qaeda in the Islamic Maghreb (AQIM).

Katsiroubas and a fellow Canadian friend, Ali Medlej, both of whom participated and were killed in the gas plant attack, are believed to have received training at an extremist camp in Mali.

The militants began their assault by attacking a bus full of foreign workers, then ramming the gates at the residential base, where they went on a door-to-door hunt for foreigners.

The vast majority of workers at the plant were Algerian. But it is jointly run by Algeria's state oil company, Britain's BP and Norway's Statoil. About 130 foreigners worked there at the time of the attack.

As they found the foreign workers, the militants tied their hands and feet. Some had their wrists bound with "detcord" – an explosive type of rope. In some cases, hostages were even made to wear explosives around their necks like a necklace.

According to an eyewitness, some of the militants posed with the workers — and a flag — and apparently made a hostage video that has not been seen in public.

Balmaceda said the militants used the hostages as human shields. When Algerian helicopters approached the plant on the second day of the hostage-taking, Katsiroubas ordered his hostages to stand in a circle and raise their hands.

Then, according to Balmaceda, as the hostage takers prepared to move the foreigners in a convoy, some of the militants — including Katsiroubas — prepped weapons for the journey, including what appeared to be improvised explosive devices.

"They are assembling the bomb, in front of us," he said.

Balmaceda miraculously survived when a militant detonated just such a device inside the vehicle in which Balmaceda was made to ride. He had been sandwiched between two spare tires.

'Do you speak English?'

One Algerian worker, interviewed by CBC News on condition of anonymity, said that when he came across Katsiroubas during the ordeal, the 22-year-old addressed him in Arabic.

"He called me using very formal Arabic, you know, the one we use only at school," said this man. "He told me 'Come here, do you speak English?' And I said no, because I reflected very quickly if I have said yes, then perhaps I would have been used as a translator.

"He said, 'We are looking for people from operations. We are looking for the expats, where are they?' I said in Arabic, 'Sorry I don't understand.' And then he said, 'OK, OK, you can go, you can go."

Until he escaped on the second day of the ordeal, the worker, who said we could call him Mohammed, would see Katsiroubas repeatedly.

"I understand he was travelling between the residential camp and the plant. He was kind of very active and very smart, very in good shape. Moving very quickly between the members of his group and asking people and so on."

The man also heard Katsiroubas give a kind of situation report over the telephone.

"He was speaking in English. I don't know to whom. But he was speaking in English, saying: 'Everything went well, we have two groups'," in an apparent reference to the hostages.

Katsiroubas and his colleagues asked a lot of questions of the workers, says the Algerian worker, like how to find the car park, where to find gasoline, and how to restart the emergency generator after the power had been cut.

American electrical engineer Cris Castro, who was hiding among a large group of Algerians, also came across Katsiroubas, and noticed him right away.

He once glimpsed Katsiroubas on the phone trying to get away from the crowd, apparently making demands of an unknown but obviously English-speaking party.

"I remember [him] mentioning on his cellphone, talking about negotiations," said Castro at his home in Houston, Texas.

"He was not yelling, he was not fast pacing, back and forth, [or] running around … [he's] talking about negotiations like he's talking about some card game.

"You know, you're talking about lives at risk. But yet he was — that's what really struck me — the calmness that they had."

"Even then I wonder what is this fellow doing here … I said he could have been an electrical engineer … geologist, doctor, some professional. You don't have to be in this business of threatening, killing people."

Mike Lovelady, an American from Nederland, Texas, whose brother Victor Lovelady was killed while riding in the same convoy as Balmaceda, also expressed bewilderment at the involvement of the Canadians.

"You could just walk by these kids and never know they were terrorists, and I just, what do you say? You just wonder why.

"It's almost hard to put your finger on the suffering, it's been so bad, and what these young men have done to many families … the holes they left in the hearts and the families they destroyed."

"Mohammed" also said he was shocked to find out later the man was Canadian.

"I can understand that a guy living in the deep south of Algeria or northern Mali, very poor, no future, joining this kind of group. But a guy living in Ontario ... I don't know. I didn't understand."