In recent years, Ali Omar Ader, a 38-year-old, self-described freelance journalist in the Somali capital of Mogadishu, had launched a publishing house that he said he wanted to turn into a think tank studying the Horn of Africa.

Unbeknownst to him, during that time he was the target of a complex investigation by Canadian police that involved wiretaps, surveillance and undercover agents.

On Thursday night, while Mr. Ader was in Ottawa, the RCMP arrested him on allegations that he was involved in the kidnapping of Amanda Lindhout, the Canadian freelance journalist who was held hostage for 15 months in Somalia.

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"He was one of the main negotiators within the group involved in this," RCMP Assistant Commissioner James Malizia told reporters in Ottawa on Friday.

He said Mr. Ader is a Somali citizen and not a resident of Canada.

One of Ms. Lindhout's former fixers in Somalia said he recognized the man.

Abdifatah Mohammed Elmi was travelling with Ms. Lindhout and Australian photographer Nigel Brennan when they were abducted off a road outside Mogadishu in August, 2008.

Mr. Elmi and two other Somalis were kept in a separate room from the two foreigners and were released a few months later. Ms. Lindhout and Mr. Brennan were released in November, 2009

Mr. Elmi alleges that Mr. Ader was present and sometimes even joined in when the captors would beat their Somali captives.

"I'm feeling very happy tonight," Mr. Elmi said when reached by telephone in Somalia.

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Some of the kidnappers covered their faces, but Mr. Ader didn't, Mr. Elmi said.

In his social-media accounts, Mr. Ader describes himself as an author and head of a publishing house in Mogadishu.

During the period when Ms. Lindhout and Mr. Brennan were in captivity, Mr. Ader said he was a "Web innovator" for the Islamic Courts Union, then self-employed.

Among the accounts he followed on Twitter were the pages for two tourism agencies, Destination Canada and the Canadian Tourism Commission.

Samir Adam, a lawyer representing Mr. Ader, said his client was arrested in Ottawa on Thursday night.

Mr. Ader made a very brief court appearance via video link on Friday as his lawyer asked for the arraignment to be put on hold for a week.

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He was charged under the Criminal Code with hostage-taking.

Assistant Commissioner Malizia said Mr. Ader was in Canada "for a few days" when he was placed under arrest. He would not say how Mr. Ader came to Canada.

A lengthy investigation, code-named Project Slype, was conducted overseas, using undercover operators, surveillance and wiretap interceptions, he said.

"This investigation posed a number of significant challenges as it was carried out in an extremely high-risk environment, in a country plagued with political instability."

One source with knowledge of the investigation said the Crown's stratagem to get Mr. Ader to Canada amounts to an intriguing one.

"It was an interesting manoeuvre, let's put it that way," the source said, without elaborating.

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Several lawyers and police officials consulted by The Globe and Mail said that, in general, Mr. Ader would likely had to have been lured to Canada, given there was no legal means of extraditing him from his turbulent home country.

They speculated such a ploy would likely have been done in conjunction with paid police agents or undercover officers and that this is not in itself novel.

In fact, just about every major terrorism prosecution in the past decade involving Canadian suspects in Canada has involved such infiltrators. Yet police were loath to publicly highlight the crucial roles played by these operatives when the suspects in these conspiracies – the "Toronto 18," "VIA Rail" and Victoria legislature cases – were rounded up. It was only later, when evidence was introduced in court, that the level of the state's infiltration became clear.

Any plans to use "extra-legal" force by military or intelligence agencies to effect an arrest in a third country would likely severely undercut any Canadian prosecution.

For example, in 2010, a U.S. bid to extradite Abdullah Khadr from Toronto to the United States failed after a judge revealed that the United States had first paid Pakistan a bounty to arrest him and hold him for interrogation, prior to his return to Canada. Mr. Khadr was "still entitled to the safeguards and benefit of the law, and not to arbitrary and illegal detention in a secret detention centre where he was subjected to physical abuse," the judge ruled as he quashed that case.

A spokesman for the Department of National Defence said the Canadian Forces, including its special forces command, were not involved "in any way" in Mr. Ader's coming to Canada.

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Assistant Commissioner Malizia thanked Ms. Lindhout and Mr. Brennan for providing witness statements that assisted in advancing the investigation. "Victims and witnesses must relive events that they should not have had to endure in the first place," he said.

He said he had been personally in touch with Ms. Lindhout to update her with the latest developments.

A representative said Ms. Lindhout was travelling and not available for an interview.

Mr. Brennan could not be reached for comment Friday. "Amazing news …" he wrote on Twitter. "Finally, justice will be served. #Karma," he wrote.

For Canadian police and prosecutors, the case may represent a new approach in files where both suspects are located and alleged offences occurred outside of Canada.

Previous cases involved, for example, war-crime suspects who were already residing in Canada.

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In the past, Canadian suspects who have committed terrorist acts in foreign jurisdictions and returned to Canada under their own volition have been successfully prosecuted under the Anti-Terrorism Act for both foreign and domestic crimes.

Such was the case, for example, in the landmark 2004 prosecution of bomb-plot suspect Momin Khawaja, who hatched parts of his schemes in Canada, Pakistan and Britain.

The RCMP have also issued warrants for suspected foreign kidnappers of Canadian citizens – such as the al-Qaeda-inspired bandits in Africa who held two Canadian diplomats for ransom in 2009.

With additional reporting from Kristy Hoffman, Verity Stevenson and Oliver Sachgau in Toronto and Kim Mackrael in Ottawa.

Editor's note: An earlier version of this story said Ali Omar Ader was apprehended abroad and taken to Canada. In fact, it is not currently confirmed how he arrived in Canada.