Hassan Diab, an Ottawa professor behind bars in France despite numerous court rulings questioning the evidence against him, is being held solely for political purposes, his lawyer said Wednesday.

Donald Bayne said France is keeping Diab behind bars so it won't be seen as soft on terrorism after a spate of recent attacks. And he said the Trudeau government is acting like a "passive little brother" to France by actively not raising his case.

"He has become, in effect, a political prisoner of the terror trauma in France," Bayne told a news conference on Parliament Hill.

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The veteran lawyer outlined what he called new evidence uncovered this week by investigating judges in France that shows Diab was in Lebanon, studying for and writing university exams, at the time of a fatal 1980 synagogue attack in Paris.

Bayne said the French investigation has found six independent witnesses who were part of a group studying with Diab in 1980. Documents from the Lebanese University confirm that Diab sat for and passed exams at the time of the attack.

The investigation also confirmed Diab's account that his passport was stolen and used by somebody else at that time, Bayne added.

Diab denies any involvement in the attack that left four dead and dozens injured.

Amnesty International, the Canadian Association of University Teachers and Diab's family question his continued imprisonment, given that French investigating judges have ruled six times he should be released on bail. All of the release orders have been overturned on appeal.

The most recent release order, in late April, noted evidence that Diab was in Beirut when the bombing occurred. A French appeal court reversed that order on May 2, which kept Diab behind bars.

Bayne accused the federal Liberal government of ignoring the evidence that he says clears Diab because its judgment is being clouded by its otherwise warm international relations with France.

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"I think there's been a deference to France. We're getting the feeling on behalf of the family that it's Canada playing the passive little brother to France," said Bayne.

"But this is the time for the Canadian government to stand up for one of its citizens."

Alex Neve, the secretary general for Amnesty International Canada, noted "the sense of camaraderie" between Prime Minister Justin Trudeau and French President Emmanuel Macron that was on full display last month at the G7 and NATO summits.

He said that provides an opportunity for Trudeau to raise Diab's case as well as ensuring his ministers are looking into it.

Neither the Prime Minister's Office nor the Global Affairs Department replied promptly to a request for comment.

Amnesty has sent letters to Foreign Affairs Minister Chrystia Freeland and Justice Minister Jody Wilson-Raybould, as well as Freeland's parliamentary secretary for consular affairs, Omar Alghabra.

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In a June meeting, Diab's wife Rania Tfaily said Alghabra told her the government was monitoring the case, but she called on it to do more.

Her husband lost the chance to witness his son's birth, and to have memories of his children's milestones in their early years of development.

"Why is there this total indifference to the suffering of an innocent man and the plight of his family?"

Bayne questioned the government's inactivity on Diab's case given it recently intervened in the case of two British Columbia winery owners "who are wealthy Canadians," and have been jailed in China on an alleged customs violation.

A Global Affairs spokeswoman told The Canadian Press earlier this month that "we have raised our concerns at a high level with Chinese authorities" about that case.

The department issued that statement when the daughter of John Chang and Lan-Fed (Allison) Lu visited Ottawa to raise support for the plight of her parents.

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Diab was removed from Canada in November 2014 after the Supreme Court declined to hear his appeal of an Ottawa's judge's order that he be extradited.

Ontario Superior Court Justice Robert Maranger said the evidence against Diab was "weak, convoluted and confusing," but that is was sufficient to meet the lower legal test of whether he should be extradited.