It was a love story between an affluent Canadian woman and an Indian rickshaw driver. They married secretly, and fearing violence from her family, fled to India. But in a village in the Punjab, 24-year-old Jaswinder ("Jassi") Kaur Sidhu, of Maple Ridge, B.C., and her husband, Sukhwinder Singh Sidhu, travelling by motor scooter, were stopped by several men. She had her throat slit, and he was severely beaten.

On Friday, the Supreme Court of Canada upheld the extradition of the woman's mother and maternal uncle to face conspiracy to commit murder charges in India – 17 years after the alleged "honour killing." (India requested the extradition in 2011.) An appeal court had ruled that the risk of mistreatment in Indian jails was too high, and that the extradition of Ms. Sidhu's mother, Malkit Kaur Sidhu, and uncle, Surjit Badesha, both senior citizens with health problems, would violate their right to security of the person protected by the Canadian Charter of Rights and Freedoms. It was a decision that the Canadian government argued put at risk all extraditions to India, and indeed to any country whose jails have been criticized by human-rights advocates.

But the Supreme Court ruled unanimously that the Canadian government had acted responsibly in seeking assurances from India that the B.C. pair, both Canadian citizens from India, would not be tortured or mistreated.

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The court said that the federal government, not the courts, has the expertise to make the decision to extradite, and as long as the decision is a reasonable one, the courts should not substitute their own views.

"The inquiry for the reviewing court is not whether there is no possibility of torture or mistreatment, but whether it was reasonable for the Minister to conclude that there was no substantial risk of torture or mistreatment," Justice Michael Moldaver wrote for the court.

Justice Minister Jody Wilson-Raybould told reporters that she had not read the ruling in detail yet, but "we, and I take great care in upholding our international extradition treaties and ensuring that decisions are consistent with Canadian values, consistent with the treaty and ensuring that any international assurances are pursued and reviewed in great detail."

University of Ottawa law professor Amir Attaran, who specializes in international law, called the ruling "gravely mistaken and naive," adding, "You cannot, you should not, apply a standard of reasonableness to the question of whether an assurance given by a foreign country is an adequate bulwark against torture."

In an interview, he said government should have to convince the courts on a much higher standard – "a standard of correctness" – that the assurance it receives are credible.

Under an international convention ratified by Canada, extraditing or deporting an individual to face torture is forbidden.

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Justice Ian Donald, writing for a majority of the B.C. Court of Appeal, had said that Indian assurances were empty. He scoffed at that country's promise of permitting Canadian consular access, saying torturers are adept at concealing what they do. He said that Canada had two options: It could seek more meaningful assurances, or could bring the pair to trial in this country.

But the Supreme Court said the justice minister at the time, Peter MacKay, had reason to believe India's promises: There was no evidence of a history of India violating its assurances to extradition treaty partners such as Canada; India wishes to maintain its extradition relationship with Canada and other partners; and Mr. Badesha and Ms. Sidhu had no religious or political affiliations that would make them particular targets.

The court attempted to occupy a middle ground, however, saying that Canada must not extradite where a substantial risk of torture or mistreatment exists, and that "general evidence" from non-government groups or others is enough to demonstrate that risk. The Canadian government had insisted that only evidence related to the actual risks facing the individuals involved would be sufficient.

"That is almost impossible given that evidence of human rights abuses is very difficult to obtain and is necessarily private and hidden from the public," Ranjan Agarwal, a Toronto lawyer representing an intervenor group, the South Asian Legal Clinic of Ontario, said in an e-mail. "The Court rightly rejected this view, and held that general evidence could be relied upon."

John Norris, a Toronto lawyer who represented an intervenor group, the David Asper Centre for Constitutional Rights, said he is concerned at the court's deference to the Canadian government on extradition matters.

"It's always concerning when international relations can be permitted to take precedence over fundamental human rights, and the Minister is given a very wide latitude to make those determinations."

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But, he said, the court also strongly affirmed the importance of carefully considering human rights in extradition cases. "You can see it as the glass is half-full or half-empty. I prefer to see it as half-full because the emphasis on human rights is an important part of the judgment."

Michael Klein, a Vancouver lawyer representing Mr. Badesha, declined to comment. Lawyers for Ms. Sidhu could not be reached.