Before he was captured by Syrian Kurdish forces in February, Canadian Mohammed Khalifa went from being a cog in the ranks of ISIS to its English language voice.

Khalifa, 35, who goes by his ISIS nom de guerre Abu Ridwan, says he would like to return to Canada provided he can bring his non-Canadian wife and their three children.

"This area is no doubt a dangerous area. I'd want to take my family out of there," Abu Ridwan told The Fifth Estate in an interview from a prison in northern Syria.

But if his return means he will likely face justice in a Canadian court, Abu Ridwan said he would rather remain locked up where he is.

"In terms of going back to be judged, then no."

While captured ISIS members and their families at home in Canada have been pleading with Ottawa for help to repatriate them home, the country's handling of the contentious issue has come in for criticism by security experts.

Watch Abu Ridwan talk about his belief in ISIS:

Former ISIS fighter on the state of the organization 0:16

For Abu Ridwan, the desire to live in an Islamic state took him out of Canada six years ago. In the summer of 2013, Abu Ridwan had graduated from Toronto's Seneca College and had a job with a tech company when he decided to leave it all behind to be a part of the emerging Islamic State in Syria and Iraq.

"I was happy coming to a place where we have an Islamic state and we could live in an Islamic state and implement the Sharia law. I was content with what I had and the life I was living."

Within a few months, he had joined the ranks of ISIS and pledged his allegiance to its leader, Abu Bakr Al-Baghdadi.

His Arabic and English language skills caught the attention of ISIS commanders and he was recruited to the group's media department headquartered in the city of Raqqa.

"We come in the morning and we leave later in the day. If you finish your work, you might leave early. It's nothing unusual if you consider how you work even in like Canada; you know if you are sick or have an emergency, you take a day off. It was very normal," Abu Ridwan said.

Watch "When terror comes home: The plan for deradicalizing returning ISIS fighters" on The Fifth Estate on CBC-TV on Sunday at 9 p.m.

Yet life was anything but normal for the civilians who lived in Raqqa. The underground citizen journalist group — Raqqa is Being Slaughtered Silently — documented 29 public civilian executions in Raqqa in November and December 2014.

Abu Ridwan said his monthly ISIS salary of slightly less than $200 US was enough to live a comfortable life.

"It's not like you're struggling and you're poor or anything. You are still living good, you were eating well."

Flames of War

Abu Ridwan told The Fifth Estate that after spending months translating and reading ISIS news items, he was given a script for a propaganda video by ISIS commanders in September 2014.

"They said we want you to read this and so I recorded it, and they took it and they asked for some changes. I rerecorded some parts, and that was it," Abu Ridwan said.

But when ISIS released that Flames of War video on social media platforms, the threats it contained against Western countries caused a panic among security agencies in Canada, the United States and Europe.

Terrorism researcher Amarnath Amarasingam has interviewed more than 50 foreign fighters and describes Flames of War as ISIS's stamp on how it wanted the world to perceive it.

Terrorism researcher Amarnath Amarasingam has interviewed more than 50 foreign fighters. (CBC)

"The video was horrific. It showed a series of executions and set the stage of what we knew of ISIS going forward in terms of its brutality and its perverse creativity in how it chose to execute so-called spies and people that it considered to be enemies of the state," said Amarasingam, an assistant professor at Queen's University in Kingston, Ont.

At FBI headquarters in Washington, D.C., an alert was issued asking the public to call in any tips, however small, that would lead to unveiling the identity of the voice.

After the fall of Raqqa to Kurdish forces backed by the United States, Abu Ridwan and his family fled to the city of Baghouz. Earlier this year, ISIS fighters held up in the city surrendered to Syrian Kurdish militia. Abu Ridwan was one of them.

Masked executioner?

Abu Ridwan told The Fifth Estate that his role in the Flames of War was limited to narrating the video and that he did not participate in any executions.

But intelligence analyst Jeff Weyers believes Abu Ridwan might be the masked executioner in the video.

Intelligence analyst Jeff Weyers suspects that Abu Ridwan is diminishing his role with ISIS. (CBC)

A masked man can be seen presiding over Syrian soldiers digging their own graves before being shot in the back of the head, their bodies tumbling into the freshly dug graves.

Weyers suspects that Abu Ridwan is diminishing his role to avoid prosecution for mass murder.

"A lot of the Western fighters are trying to diminish their responsibility — I am a chef, I am a cook, I am a driver. Well, there are a lot of chefs, cooks and drivers right now and not a whole lot of fighters that helped the Islamic State take over all this territory," Weyers said.

Geolocating a crime scene

Weyers said Canadian authorities can take steps to determine whether Abu Ridwan was the executioner in the ISIS video.

"Even wearing a mask, you are still revealing portions of your face. The eyes are enough that you can do an identification."

Another method is using ISIS's own video to pinpoint the exact spot where the massacre took place. It's a technique called "geolocation."

Weyers said he spent hours pouring over the Flames of War video identifying landmarks and managed to locate the precise spot where the massacre took place.

He said he gave the information to the RCMP but is not aware whether anything was done with it.

Captured ISIS recruits

Amarasingam said Abu Ridwan is one of six Canadian men being held in prisons at undisclosed location in parts of northeastern Syria, in territory controlled by the Syrian Democratic Forces.

Nine Canadian women, often described as ISIS brides, and 18 children are being held at either Al-Roj or Al-Hawl, overcrowded refugee camps in northeastern Syria.

ISIS wives and children were rounded up in Syria and taken to detention camps earlier this year. (Getty Images)

The captured ISIS members and their families here in Canada are pleading with Ottawa to help bring them home.

U.S. President Donald Trump has repeatedly threatened that they would be released if Canada and European countries don't repatriate their nationals.

Ralph Goodale, Canada's minister of public safety, says the captured ISIS members "have a constitutional right to re-enter the country, but the government of Canada does not have a legal obligation to facilitate their return."

But Canada's approach has been criticized by some security experts.

Watch a security expert talk about Canada's policy:

A security expert on Canada's policy 0:18

Leah West, a former lawyer with the federal Department of Justice, describes the country's policy as one of "inaction."

Canada "should bring them home and prosecute those that they have the evidence to prosecute for offences," said West, who teaches national security and intelligence at Carleton University in Ottawa.

Even though Abu Ridwan is confined to a Syrian prison, he told The Fifth Estate he has no regrets about the oath he took to defend and fight for the Islamic State.

"In terms of actually being a part of the Islamic State, I don't regret that," said Abu Ridwan.

"The fact that I'm a prisoner doesn't mean that I change my beliefs. It doesn't mean that I change my position with regards to my religion, with regards to the Sharia."

Another Canadian ISIS fighter who goes by the nom de guerre Abu Huzaifa said he spent seven months enforcing Sharia law for ISIS before returning to Canada in 2016.

In an interview with a New York Times reporter, Abu Huzaifa confessed to killing civilians in Syria, but he has not been charged with any crime.

Abu Huzaifa posted this photo of himself on his Instagram page shortly after he returned to Canada in 2016. (Abu Huzaifa/Instagram)

The Fifth Estate approached Abu Huzaifa with a hidden camera at the place where he works in the Greater Toronto Area. He said he is in a counselling program with a local imam that is monitored by the RCMP and aimed at deradicalizing him.

Abu Huzaifa said he is not sure how the sessions are going or whether they are making any difference for him.

When asked what he thought about the captured ISIS fighters in Syria, men he still describes as "his brothers," he said: "If we bring these guys back, it shouldn't be that big of a problem, to be honest. I'm probably scarier than them walking around free because day by day I know I got off scot-free."

Watch the full episode of The Fifth Estate: