SAN SEBASTIAN — On Jan. 14, 2015 prosecutor Alberto Nisman went on TV to accuse Argentine President Cristina Fernández de Kirchner of negotiating the impunity of Iranians accused of the Buenos Aires’ 1994 AMIA bombing, the biggest terrorist attack in the Western hemisphere before 9/11.

“There was an alliance with terrorists, negotiation with a state that bought the terrorists and the terrorists themselves,” said a dapper Nisman, in the interview which appears in the early stretch of Justin Webster’s deeply-caring, meticulous “The Prosecutor, the President and the Spy,” a six-hour doc series which world premiered Monday at Spain’s San Sebastian Film Festival.

Four days later, and on the eve of testifying in court, where he promised decisive proof of the collusion, Nisman was found dead in his bathroom with a single shot to the head. His death reverberated around the world.

Immediately, Kirchner is accused of ordering Nisman’s murder. She denounces the man described in “The Prosecutor” as Argentina’s Rasputin, the fearsome Antonio Horacio “Jaime” Stiuso, a spy with close links to the CIA and Mossad, of conspiring against her.

Produced by Barcelona’s Justin Webster Productions and Fasten Films, Berlin’s Gebrueder Beetz Filmproduktion and backed by Movistar+, ZDFinfo and DR,  “The Prosecutor, the President and the Spy” is “a story of ambition, corruption and espionage which unfolds, with rival narratives of good and evil, of suicide or murder, and of truth itself, around a body found in a bathroom, with enormous international resonance,” its makers say.

“The Prosecutor” will be “an earthquake” in Argentina, predicts San Sebastian Festival director José Luis Rebordinos.

It is also Webster’s most original and most ambitious series to date – building on “Death in Leon,” the Emmy-winning “Six Dreams” and HBO España’s “The Pioneer” – marking the full emergence of an auteur and the creative and industrial potential of a form of story-telling with which he admits he’s obsessed: Cinematic non-fiction series.

That cinematic quality is seen from the get-go. To the gentle thud of ominous music, a camera steels at night at height past the chic glinting black tower-blocks of Buenos Aires’ luxurious Puerto Madero, then into an apartment, over markers lying on ministerial papers on a desk, towards a bathroom, as an emergency service call cuts in with a woman’s voice saying she’s found the body of prosecutor Nisman.

“The Prosecutor’s “thrust is to reach some more clarity on a subject that is so difficult, and so complex.. As often happens, in lots of cases, they play out over a long period of time. People have strong opinions about it, but they don’t really know the whole story,” says Webster.

So “The Prosecutor” lays out the whole story, but with no authoritative voiceover telling the audience what to think.  Suicide or murder? Audiences “have to figure out [their conclusions] coming to much more reasonable ones, having seen  the series They may well come to a conclusion, one open to interpretation, though it not for me to say,” Webster says.

Film forms abound. “The Prosecutor” packs footage of Nisman and Kirchner – who never said no or yes to interview – with key interviewees, led by “Stiuso” himself – charming, evasive – and the doughty Viviana Fein, the prosecutor on the Nisman case over 2015-16, who recognized his death’s suspicious circumstances but baulked at ruling it murder for lack of proof.

Other key witnesses, 14-15 of 50 interviewees in all, take in Hector Marcos Timerman, Argentina’s minister of foreign affairs, 2010-15, who proposed a joint commission between Argentina and Iran to advance on arrests for the AMIA bombings; Diego Lagomarsino, Nisman’s IT technician, who gave Nisman the gun that ended his life; even Alberto Fernández, chief of staff 2003-08, under Nestor Kirchner, and now the frontrunner president candidate in Argentina’s Oct. 27 elections.

Yet this is not at all a talking heads documentary. As interviewees reflect to the camera, the film flips to quick-cut footage, evoking a mood, or giving more visual detail- the AMIA center debris after the bombing; photos of the main suspect, according to Nisman and Stiuso, in the AMIA bombing; or even counterpointing observances. As Nisman’s death becomes highly politicized, and Kirchner fights back, accusing AMIA’s investigators of failing to solve the attack, the camera cuts to shots of Nisman’s funeral cortege.

There’s re-creation. Of Nisman taking a taxi to his fateful TV interview, for example. But it’s deft and brief. “If you’re telling a story like this, it’s important to stay in the present tense, thinking about the overall story,” Webster says. He adds: “You don’t want to stop the narrative, stay with somebody in the room for a long time.”

“The Prosecutor, the President and the Spy” says a lot about how geo-political sea change – Obama’s detente with Iran, for example – seeps down to national affairs, leaving Nisman suddenly on a limb when he still pressed for AMIA-related arrests.

It paints a less than glamorous portrait of intelligence services. “During the dictatorship, state intelligence was part of the repression. In democracy, Argentinian state intelligence keeps working for the CIA and also works for the President,” says Luis Moreno Ocampo, Chief Prosecutor of the International Criminal Court, 2003-12.

“How?” he asks. “It helps by using secret funds which leave no trace. These funds allow them to give money to their friends and attack their enemies.”

Above all, however, “The Prosecutor, the President and the Spy” uses the basic resorts of storytelling to shed light on the Nisman case.

“The rules with fiction and non-fiction are completely different in a sense of the relationship with the truth. A good non-fiction story is showing you “this much is true,” uncovering the details, the evidence,” says Webster.

He adds: It’s not like there is one version of the truth and another version of the truth, there is only one truth.”

Yet, he says, “I strongly believe that in non-fiction and fiction, the way of telling a story well is the same. And you tell it through the characters, you tell their story.”

“The Prosecutor…” begins with the AMIA bombing, not just because Nisman accuses Kirchner of a cover-up but also because he served as a special prosecutor in charge of the AMIA bombing investigation from 2004 to 2015. Investigating them –  and the series shows extended footage from their extraordinary hearings which take a dramatic turn –  Nisman, for some at least, won his spurs, helping to secure a 2007 Interpol red alert calling for the arrest of six individuals, five high-ranking Iranian politicians – accused of involvement in the terrorist attack.

In episode after episode, however, “The Prosecutor, the President and the Spy” peels away public persona – Nisman’s, Stiuso’s in interview – to reveal figures of almost Shakesperian proportions and complexity. It is only through a comprehension of their characters that audiences may reach a conclusion, however open to debate, about a death that has mesmerized and polarized Argentina.

Murder or suicide? “The Prosecutor, the President and the Spy” leaves the audience to decide. While reflecting a spectrum of opinions, a building through-line of argument, testimony and painstaking recreation of events – especially in Ep. 4. “Five Days”-  does, however, suggest a plausible conclusion.