Who wanted Alberto Nisman dead? He was found slumped on his bathroom floor, the door locked from within,  a gun beside his inert body. The trajectory of the bullet and Nisman's fingerprints on the pistol seemed consistent with suicide.

But had he been "suicided"? After all, Nisman's investigation of the 1994 bombing of a Jewish community centre that killed 85 people had led him to lodge an explosive 289-page criminal complaint accusing Argentina's President, Cristina Fernandez de Kirchner, and Foreign Minister, Hector Timerman, of conspiring with Iran to allow the terrorists behind the bombing to go free. The pay off was a lucrative trade deal: Iran would buy Argentinian wheat and sell it cheap oil.

Is it conceivable that Kirchner, or her political allies, would silence their relentless critic? Or had Nisman passed his use-by date for a disgruntled former intelligence boss who, some say, was manipulating him?

Two-thirds of Argentinians are convinced Nisman was murdered and, polls indicate, half of them reckon that somehow their president did have a hand in it. But Iran is in the frame too, perhaps because Nisman's renewed accusations came at a critical stage in the global negotiations over its nuclear ambitions.

Might Nisman's murder have been a proxy strike in a global conflict - Iran or Hezbollah taking a shot at Israel? Was it suicide - after a decade in which he had failed to punch through in one of Argentina's most high-profile investigations, did the pressure just become too much for Nisman?

The blaze of publicity around his death has cast light into many dark corners. There's a war within the intelligence services - split for and against Kirchner's government.

Also, there's great tension within the Jewish community – apart from Nisman, Argentine Foreign Minister Hector Timerman is Jewish and so too is judge Daniel Rafecas, who just weeks after Nisman's death rejected the prosecutor's accusations against the president and the foreign minister as lacking "even circumstantial evidence".

Then there's the international dimension. Washington and Tel Aviv, and their respective intelligence services, saw the outcome of Nisman's work as vital to their interests. All the suspects in the 1994 bombing - principally Iran and, for a time, Syria - hailed from the Middle East.

As has been the case for almost 21 years, the Argentinian investigation into the Asociacion Mutual Israelita Argentina (AMIA) attack seemed to be going precisely nowhere when, in January 2015, a legal thunderclap was heard in Buenos Aires.

In a series of media interviews, Nisman revealed the existence of a 289-page criminal complaint, in which he accused Kirchner and Timerman of a breathtaking conspiracy to put the alleged perpetrators of the 1994 bombing beyond the reach of Argentinian law. It was, he said, a dirty deal that was to be sweetened with a trade exchange in which Buenos Aires would sell Argentine grain to Iran and, in return, get Iranian oil at a discount.

Claiming to have "irrefutable proof", Nisman declared that Kirchner and Timerman were the "authors and accomplices of an aggravated cover-up and obstruction of justice".

Relying on thousands of hours of phone-taps of supposed go-betweens - not of Kirchner and Timerman themselves - Nisman alleged a conspiracy that failed only because, firstly, Interpol had refused to lift arrest warrants out for five high Iranian officials, and secondly an Argentine court had shot down a proposed truth commission, in which Tehran and Buenos Aires had agreed to jointly appoint a team of international jurists to examine the bombing.

Timerman countered with powerful arguments - an email from the recently retired head of Interpol, confirming that Timerman had not requested that the Iranian warrants be lifted; that only the issuing judge could ask for the warrants to be lifted, not a politician; that it was he who had asked Washington to include the need for a breakthrough on the AMIA bombing in the US-led nuclear talks with Iran; that Iranian oil had too high a sulphur content for Argentina's refineries; and that Argentinian grain was sold abroad by the American agri-giant Cargill Inc, not by the Buenos Aires government.

Nisman, Timerman also explained, had to be aware that he was snookered by the law in both countries. Under a constitutional provision dating back to the time of the Shah, Iran could not extradite its citizens to a third country; and under Argentine law, a suspect could not be tried in absentia. The truth commission was to serve as an essential circuit breaker, allowing an Argentine judge to go to Iran to interview the suspects.

Despite all this, New York's Jewish Daily Forward reported in the US: "Some in the community say [Timerman] is a traitor to Judaism."

When the truth commission deal became public in 2013, Timerman came under ferocious attack. Asked at the time how he could sign a deal with Iran, a country whose president had denied the Holocaust, he replied: "I did not meet with the Iranians to discuss the Holocaust – I was with them to solve the AMIA case."

Rabbi Sergio Bergman, an opposition MP, is demanding that the foreign minister be hauled before a Jewish ethical tribunal.

But as the Forward's website reported: "Some scholars and members of the Jewish community have defended Timerman. AMIA and other Jewish organisations, they say, have never genuinely sought justice for the victims of the bomb attack during an investigation marred by setbacks, and a corruption scandal involving a former president and a prominent Jewish leader. They have also cast suspicion on Nisman's focus on Iran, claiming that other lines of investigation were discouraged by foreign influence."

Last year, Israel's ambassador to Buenos Aires at the time of the AMIA bombing, Itzhak Aviram, claimed that Israel had already assassinated the perpetrators. Prompting furious denials by Tel Aviv, Aviram was quoted as saying: "The large majority of those responsible are no longer of this world – and we did it ourselves."

Some who read the detail of Nisman's allegations were underwhelmed, particularly by an absence of legal rigour in charges against two of the most senior people in the country. Horacio Verbitsky, a renowned investigative reporter who now heads the country's leading human rights group, wrote in The New York Times: "Of the 290 pages, only two mentioned possible violations of the law, and there was no reference at all to legal doctrine or jurisprudence . . . many people believe that the document wasn't written by a lawyer and that Mr Nisman was misled and used."

In the days before his death, Nisman was upbeat. He reportedly texted to friends: "What I'm about to do now had already been decided a while ago, and I'm prepared for this - I do it convinced that it's not going to be easy. Completely the opposite, but sooner or later, the truth will triumph."

But he also seemed to foretell his own demise. Nisman told one reporter: "I could come out of this one dead." To another, he said: "Regardless of whether or not Nisman is here or not, the evidence is there."

The 51-year-old - variously described by colleagues and friends as professionally obsessive, secretive and compulsive - had joined the AMIA investigation as early as 1997, surviving with his reputation intact when video surfaced showing the investigating judge offering a prospective witness $US400,000 to give particular evidence. The case collapsed spectacularly - the suspects, including 19 policemen, walked free; the judge was impeached.

A decade on from the bombing, then Argentine president Nestor Kirchner tried again, setting up a team that grew to 60 or more. Describing the investigative failure as a "national disgrace", he installed Nisman to lead the new team.

By 2006, Nisman had concluded that the attack was an Iran-Hezbollah operation and, at his instigation, Interpol issued arrest warrants in 2007 for former Iranian president Ali Akbar Hashemi Rafsanjani; Iran's defence minister Ahmad Vahidi; and a former commander of the Revolutionary Guard, Mohsen Rezaei.

At that time, the newly appointed President Cristina Fernandez de Kirchner was reaching out to Iran and Nisman was complaining that official Argentinian support was falling away. Late last year Nisman was seen to be even more isolated when Kirchner sacked Antonio "Jaime" Stiusso, the director of counterintelligence, who Kirchner later claimed  had been feeding suspect information to the prosecutor.

"Stiusso's information, which steadily implicated the president in some nefarious detente with Iran, is widely thought to have come from US and Israeli intelligence services," The New Yorker reported. But as revealed in diplomatic cables leaked by WikiLeaks, Nisman did not need a chaperone to get to the Americans – he regularly consulted the US embassy, tipped off diplomats on what he would be doing, even shared drafts of his work – and would revise them in line with the American critique.

On January 14, Nisman went public with his intention to lay charges against Kirchner and Timerman. In doing so, he surprised colleagues to whom he had observed earlier  that to go after the pair while they were still in office "would look like political interference".

Suddenly, he had abandoned a long-planned ski vacation with his daughter in Europe because, one of his associates was quoted as saying, he worried that Argentina's attorney-general was about to remove him from a "case, [that] for him, was his life".

Nisman had received many threats and had been assigned a 10-man security detail - and he had two guns of his own. But now he wanted another gun. A colleague gave him a Bersa Thunder .22 handgun. When he was found it lay beside him.

There's been no explanation for why Nisman's guards were absent - but seemingly he sent them away on the day; there was no gun residue on his hands; there was a shopping list for his housekeeper, but no suicide note; the CCTV at his apartment complex revealed no suspicious visitors; detectives seemed underwhelmed by a footprint they found in a passageway that led to the apartment's air-conditioning unit.

At first Kirchner was adamant that it was a suicide. Then she was equally adamant it was a murder, in which she was the victim because "they" had used Nisman when he was alive "and then they needed him dead". She claimed that the faction in the intelligence services that was against her might have wanted "to lay a corpse at [my] feet".

The prosecutor investigating Nisman's death was more nuanced. Announcing that an autopsy found "no intervention" by others, Viviana Fein hesitated, refusing to rule out the possibility that Nisman was "induced" to suicide.

Whether out of loyalty to a slain colleague or a genuine belief in Nisman's work, prosecutor Geraldo Pollicita took the dead prosecutor's brief on the AMIA bombing to federal court - only to see it tossed aside in a withering dismissal by Justice Daniel Rafecas. It was, the judge declared in a 63-page decision, "alarmingly" shoddy; "not even circumstantial evidence"; and there was no proof that the government had asked for the Iranian warrants to be cancelled. Nisman's own evidence contradicted his accusations so "categorically and conclusively", Rafecas ruled, that there were no grounds to proceed against Kirchner or Timerman.

An appeal has been lodged by those who decried Rafecas' decision as rushed and a missed opportunity. But the aspects of Rafecas' CV that had caused many to cheer when he was allocated the case continued to apply as the same people criticised his decision.

He had courageously taken it up to the government in a recent corruption case, to the point of ordering a raid on the vice-president's apartment; and he was a respected member of the Jewish community - a Holocaust scholar invited as a guest speaker at the reconstructed Jewish community centre on the 17th anniversary of the AMIA attack.

Nisman's allegations and his death and Timerman's conduct as foreign minister have split the Jewish community and left survivors and the families and friends of victims of the two bombings questioning if more than 20 years of detective work has brought justice any closer.

Billing Nisman's demise as "the latest act in the Iran-Israel saga", an analysis in the Israeli daily Haaretz in the days after the discovery of the prosecutor's body concluded: "One day someone will write a book or a play on the confrontation between the two proud Argentine Jews, Alberto Nisman and Hector Timerman.

"Their lives embodied so many tensions, dilemmas and tragedies related to a tenuous Jewish existence in a dangerous environment. Nisman dedicated years of his life and perhaps died when trying to uncover the truth behind the death of so many Jews, taking on the establishment in his homeland.

"Timerman, the human rights defender whose father was saved from the clutches of a previous government of Argentina - thanks to the dirty dealings between it and Israel - who then joined another government, turning his back on the Jewish community and making common cause with one of the worst regimes in the world.

"Both men claimed above all to be Argentine patriots and will be remembered by history as two conflicted Jews."

REVENGE THEORY
The Israeli journalist and security analyst Yossi Melman speculates that Nisman's death might have been revenge for what was presumed to be an Israeli air strike in Syria, just hours before Nisman's body was found, in which six Iranian officers and six Hezbollah commanders were killed - one of whom was a young man called Jihad Mughniyah.

Mughniyah, Melman notes, was the son of Imad Mughniyah, the international operations chief for Hezbollah cited as the mastermind behind a series of terrorist attacks around the world - most notably, the bombing of the Israeli embassy in Buenos Aires in 1992, in which 29 people died; and two years later, of the AMIA Jewish community centre in the Argentine capital in which 85 more were killed.

Those attacks were Hezbollah's revenge for another Israeli air strike, in February 1992, in which its then leader, Abbas Musawi, was eliminated. Mughniyah snr was assassinated in what The Washington Post reported was a joint Israeli-US operation in Damascus in 2008 – by a remotely-detonated bomb planted in his car.