An earlier version of this article incorrectly characterized the defense counsel for Hamid Nouri. Nouri is represented by a Swedish lawyer. This version has been updated.

On Nov. 9, a 58-year-old Iranian lawyer by the name of Hamid Nouri arrived at Stockholm’s international airport. His papers were in order; he was traveling on a visa issued by Italy, good for the entire Schengen Area of the European Union. So he must have been startled when Swedish officials took him into a room and began to interrogate him about his past.

Nouri is still in detention today, awaiting a decision by Swedish prosecutors on whether he should face trial for allegedly participating in crimes against humanity. He stands accused of abetting the execution of thousands of political prisoners in Iran in 1988 — a crime for which no senior official in that country has ever faced official accountability.

Iranian operatives have been convicted in the past of crimes they’ve committed in France or Germany. But this is the first time that a high-ranking Iranian will face charges under the concept of universal jurisdiction — the same principle underlying the prosecution of ex-Chilean dictator Augusto Pinochet in Spain starting in 1998. “In this case, we’re talking about the Swedish court asserting jurisdiction over crimes that took place in Iran 31 years ago,” says Iranian-born British lawyer Kaveh Moussavi. “If you commit crimes that are basically an outrage against the conscience of humankind, then expect humankind anywhere on the planet to assert jurisdiction.”

That alone would already make this an extraordinary case. Even more remarkable, though, is the fact that Nouri’s arrest comes as the result of long years of painstaking preparation by human rights activists. At a time of rising authoritarianism around the world, the case in Stockholm reminds us that courageous private individuals still have the capacity to challenge even powerful states.

Iraj Mesdaghi, a former Iranian political prisoner who survived the 1988 massacre, has spent years researching crimes committed by the regime in Tehran — and tracking the movements of the perpetrators. Roya and Ladan Boroumand run a Washington-based foundation that documents Iranian human rights violations. And Moussavi is a scholar of human rights law who has worked for years on the problem of how to secure justice for the victims.

According to his accusers, Nouri was working 31 years ago as an assistant prosecutor in Iran’s prison system. In the summer of 1988, as the Iran-Iraq War was winding down, the Iranian leadership dispatched special teams of security and judicial officials known as “Death Committees” to the prisons to organize the executions of members of the Mujahideen-e Khalq (People’s Mojahedin), an armed opposition group. Thousands of prisoners were hanged, sometimes strung up from construction cranes. Their bodies were buried in mass graves, their relatives forbidden from mourning them. A second wave of executions targeted left-wing prisoners. Nouri, his accusers say, was a direct participant in the killings.

In 2009, the Abdorrahman Boroumand Foundation commissioned Geoffrey Robertson, a British lawyer who headed an international tribunal on Sierra Leone’s civil war, to conduct an inquiry into the 1988 killings; Mesdaghi located witnesses who provided testimony. A 2011 symposium at Oxford University, co-sponsored by the Boroumands, produced a set of legal opinions on how to bring the architects of the massacre to justice. At one point, Moussavi recalls, Mesdaghi posed a dare: If I can tell you that one of these men is coming to the West, will you bring him before a court?

“I took him up on it,” says Moussavi. “And on October 17, eight years later, he gave me a call.” Mesdaghi’s sources — whom he cannot disclose — had tipped him off that Nouri was coming to Europe. Drawing on the 2011 symposium, Moussavi prepared a case file, including witness testimony, that he successfully presented to the Swedes. Now, Nouri — who is being assisted by a Swedish lawyer — is awaiting the next phase of the process. Next month, the Swedish prosecutors will decide whether to allow the case to proceed to a full trial.

The story is already resonating back in Iran. Iranians who avidly consume Farsi-language satellite TV and radio broadcasts immediately understood its ramifications.

Mesdaghi vividly described to me the brutality he and others endured in those prisons at the time. But when I asked him what outcome he wishes for Nouri, he swore off a desire for revenge. “I want him to be tried fairly,” he told me. “In Sweden, he has all his rights. He will have a lawyer; I didn’t have a lawyer. I was in solitary confinement; he’ll be imprisoned under good conditions.” (Nouri claims that he’s the victim of a case of mistaken identity.)

Mesdaghi explained that his own experiences at the hands of an oppressive state have made him an opponent of the death penalty. He says that all people deserve justice — including criminals, who also have their rights. “I’m fighting for justice, not just for myself but for everybody. It doesn’t matter who you are. I’m against torture. It doesn’t matter who you are.”

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