The man who was the subject of a "preventive" arrest by the RCMP on Saturday was behind a Twitter persona that underwent a "dramatic change" in the summer of 2015, according to counter-terrorism researchers.

Kevin Omar Mohamed, 23, detained on fears of terrorism Saturday, went by the name "Abu Jayyid" online, according to the co-director of a study of foreign fighters at the University of Waterloo, Amarnath Amarasingam.

Mohamed, who has been charged with possession and concealment of a weapon — a knife, according to his lawyer, Anser Farooq — has not been charged with any terrorism-related offences.

CBC News has confirmed that Mohamed attended the University of Waterloo and, according to Farooq, was a student there for at least two years.

When the RCMP announced their arrest of Mohamed on Saturday, Amarasingam confirmed with a friend of Mohamed's that the photo of him circulating online matched Abu Jayyid's account; that Mohamed was the man behind the account.

Abu Jayyid came up on the radar of Amarasingam and his colleague at the Canadian Network for Research on Terrorism, Security and Society, Lorne Dawson, last year for statements he made online that appeared to support ISIS, something the two researchers are used to seeing in those they track online.

'Change of allegiance'

When he learned that Abu Jayyid was a University of Waterloo student, Amarasingam reached out to some of his friends. They described Mohamed as "a bit of a loner" who had some "weird views."

But Dawson says that in June 2015, Abu Jayyid suddenly stopped following anyone who was seen to be supporting ISIS on Twitter, throwing his support instead behind the al-Qaeda affiliate group, Jabhat al-Nusra.

"In June of last year, he suddenly stopped supporting ISIS," Dawson told CBC News. "He seemed to [undergo] some kind of dramatic change of allegiance."

Lorne Dawson, Professor in the Department of Sociology and Legal Studies at the university of Waterloo, says that in June 2015, Abu Jayyid suddenly stopped following anyone who was seen to be supporting ISIS on Twitter, throwing his support instead behind the Al Qaeda affiliate group, Jabhat al-Nusra. (CBC)

Al-Nusra fighters have tended to celebrate attacks carried out against the West, but unlike ISIS, the group doesn't call for attacks abroad.

"He wasn't concerning to me, because he seemed mostly to be engaged in a theological and intellectual engagement with issues of jihad and Syria," Amarasingam told CBC News on Sunday.

Abu Jayyid's transformation also caught the attention of former CSIS counterterrorism operative Mubin Shaikh, who also exchanged messages with the Twitter account since as early as April 2015.

"What's interesting is that he was very open with me. He didn't seem to have a problem with me," Shaikh told CBC News.

To Shaikh, that was a good sign.

Abu Jayyid's transformation also caught the attention of former CSIS counter-terrorism operative Mubin Shaikh, who also exchanged messages with the Twitter account since as early as April 2015. (CBC)

"A person who would be having such an open conversation with me — following me on Twitter whether other extremists could see that he's following me on Twitter — that tells me that this guy's inclined to listening to the perspectives that somebody like me would have."

Shaikh was a paid agent of the Crown who worked for the RCMP in the arrest of the so-called Toronto 18.

'Extreme statements'

On March 24, two days after the attacks in Brussels, Belgium, Abu Jayyid posted a tweet asking how to modify a popular and violent video game to be set to the scene of the Brussels airport.

It's unknown what the intent of the post was, but according to Shaikh, it just might have been what set off alarm bells for the RCMP.

A tweet asking how to change a popular and violent video game to include the Brussels attacks was posted from an account that Amarasingam and Shaikh say belongs to the Ontario man arrested on Saturday over fears of terrorism. (Twitter)

"All kinds of kids play those kind of games every day. That in itself is not a problem," Shaikh said. "But the day after a terrorist attack in a Belgian airport, and you show a screenshot of an airport being shot up — that's so closely linked.

"Anybody saying something that shows sympathy for that attack is going to (get a) visit from the government," he said.

Police have said Mohamed was taken into custody "pursuant to Section 810.011 [of the Criminal Code], Fear of Terrorism Offence."

On Saturday, Farooq told CBC News that the RCMP alleged his client encouraged and facilitated terrorist activity through the use of social media.

"It's an interpretation of the context and the words uttered by him in a social media context," he said.

Farooq would not confirm whether the Twitter account belonged to his client.

For Dawson, Mohamed's arrest came as somewhat of a surprise.

"There's some people that we deal with who make some pretty extreme statements and nothing ever happens with them; and then there's some individuals who we think of being not particularly threatening or dangerous who suddenly find themselves arrested or being visited by the authorities."

Mohamed remains in custody since his charge and is set to appear at a Brampton, Ont., court Tuesday morning.