What does international law say about targeted killings?

It certainly wasn't the first time a government was accused of orchestrating a killing on foreign soil, but observers around the world were nonetheless shocked by Prime Minister's Justin Trudeau's allegation on Monday that India's leaders had a hand in killing a Canadian citizen earlier this year in B.C. 

India has strongly denied any connection to the killing of Sikh leader Hardeep Singh Nijjar, who had been labelled a terrorist by New Delhi over his support of an independent Khalistani state. 

Such killings are usually pinned on the likes of Saudi Arabia or Russia. 

But extra-territorial assassinations aren't just for rogue states and can sometimes even be justified under international law. Sometimes. 

If the Indian government did play a role in killing Nijjar, it would be a significant violation of Canada's sovereignty. 

"There is no question that this conduct is unlawful," said Leah West, an associate professor of international affairs at Carleton University's Norman Paterson School of International Affairs. "It is an unlawful violation of sovereignty, it's an unlawful exercise of the state's power inside Canada.

"It is really hard to think of examples that are more significant than a foreign state executing a Canadian citizen on Canadian territory for their own ends."

If the allegations are true, India would be guilty of violating the basic rule that states are bound to respect each others' territorial sovereignty, said Dapo Akande, professor of public international law and co-director of Oxford University's Oxford Institute for Ethics, Law and Armed Conflict.

"Essentially what [Ottawa is] saying is, 'You've broken this by undertaking acts on the territory of Canada without the permission of Canada.'"

It would also violate the UN Charter, which says all members shall refrain "from the threat or use of force against the territorial integrity or political independence of any state."

That means if there's enough of a connection between the killers and "some sort of state apparatus in India … India itself could be held legally accountable," said Noah Weisbord, an associate law professor at McGill University and author of The Crime of Aggression: The Quest for Justice in an Age of Drones, Cyberattacks, Insurgents, and Autocrats.

Al-Qaeda's leader Osama bin Laden was shot and killed in 2010 in a Pakistani compound by U.S. Navy SEALs. Ten years later — in one of the most recent and high-profile extra territorials killings — it was the U.S. again that killed Iranian Gen. Qassem Soleimani with a drone strike in Iraq. 

Israel too has acknowledged targeting Palestinian militants, mostly through drone or airstrikes. But it also is suspected of being responsible for killing top Iranian nuclear scientists in an effort to thwart that country's nuclear ambitions.

Israel also kidnapped and eventually executed Adolf Eichmann, one of the key Nazis responsible for orchestrating the Holocaust, near his home in Argentina in 1960. (Argentina was outraged and the UN agreed the incident had violated its sovereignty.)