Zahra Kazemi's son can't overcome state immunity to sue the government, or Iran or key Iranian officials, for allegedly torturing and killing his mother, Canada's top court says.

Stephan Hachemi has devoted the past decade to raising awareness about his mother's story since her death in 2003.

But in the decision released Friday, the Supreme Court of Canada says the law excludes redress for torture committed outside Canada.

"State immunity is not solely a rule of international law, it also reflects domestic choices made for policy reasons, particularly in matters of international relations," Justice Louis LeBel wrote in the 6-1 decision.

"Canada's commitment to the universal prohibition of torture is strong. However, Parliament has made a choice to give priority to a foreign state's immunity over civil redress for citizens who have been tortured abroad. That policy choice is not a comment about the evils of torture, but rather an indication of what principles Parliament has chosen to promote."

The State Immunity Act prohibits lawsuits against foreign states in Canadian courts.

The justices handed the issue back to the government, saying legislators could change the act and open the door for Hashemi's civil lawsuit.

"Parliament has the power and capacity to decide whether Canadian courts should exercise civil jurisdiction," Justice Louis LeBel wrote for the majority. "Parliament has the ability to change the current state of the law on exceptions to state immunity, just as it did in the case of terrorism and allow those in situations like Mr. Hashemi and his mother's estate to seek redress in Canadian courts. Parliament has simply chosen not to do it yet."

The court was referring to the government 2012's Justice for the Victims of Terrorism Act, which amended the immunity act to allow victims of terrorism to sue states that are listed supporters of terrorism.

Son 'extremely disappointed'

Hachemi was disappointed with the ruling and is calling on Parliament to amend the State Immunity Act.

"While we are extremely disappointed with the majority’s ruling and its treatment of the fundamental principle of access to justice in a case that the majority itself characterized as 'horrific,' we echo the call to Parliament to amend the State Immunity Act to put an end to impunity for torture," Hachemi's lawyers, Mathieu Bouchard and Kurt Johnson, said in a written statement.

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Zahra Kazemi died in 2003 in Iran's notorious Evin Prison. (Canadian Press)

The opposition New Democrats said they would renew their calls for such an amendment.

"I find it puzzling that the government has been able to change the State Immunity Act when it comes to cases of terrorism, but not for those who are victims of torture," said NDP foreign affairs critic Paul Dewar. "It's not consistent in terms of our values."

Justice Minister Peter MacKay's office had no comment except to say that it was reviewing the ruling.

The Canadian Centre for International Justice also called on Parliament to act.

"We had hoped the court's ruling would be more responsive to the growing need of families and survivors to obtain redress but now, if Parliament doesn't act, Canadian torture survivors will likely never achieve justice," said Matt Eisenbrandt, the centre's legal director.

The Supreme Court said that state immunity "is a complex doctrine that is shaped by constantly evolving international relations" and it wasn't prepared to wade in.

"Determining the exceptions to immunity requires a thorough knowledge of diplomacy and international politics and a careful weighing of national interests," the ruling stated.

"It is not, however, this court's task to intervene in delicate international policy-making."

Allegedly tortured in Evin Prison

Kazemi, an Iranian-born Canadian photographer, was arrested and detained in the notorious Evin Prison in Tehran in 2003. She was allegedly tortured and sexually assaulted by Iranian officials, and later died. Her body was never returned to Canada.

Hachemi and Kazemi's estate filed a civil lawsuit seeking damages for her death in 2006, but the Iranian government, citing the principle of state immunity, argued it is exempt from pursuit in Canadian courts.

Hachemi countered with a constitutional challenge arguing that if the act barred their claims, it would be going against the Canadian Bill of Rights as well as the Canadian Charter of Rights and Freedoms.

The Canadian government intervened, saying if Hachemi is allowed to sue Iran, Canada could lose its immunity abroad and that relations with other countries could suffer.

The case went to the Supreme Court last December following a ruling in 2012 from the Quebec Court of Appeal.

Justice Rosalie Abella was the dissenting voice on the decision, arguing Hachemi should have the right to sue.

With files from The Canadian Press