Alberto Nisman, the prosecutor investigating the 1994 bombing of the Argentine-Israeli Mutual Association community center, talks to journalists in Buenos Aires, Argentina, on May 29, 2013.  (Natacha Pisarenko/AP)

You don't have to be a conspiracy fanatic to be gripped by the death of Argentine prosecutor Alberto Nisman late Sunday. Just a few days before he was found dead in his apartment, apparently of a gunshot wound, he himself had made an ominous prediction to a journalist: "I might get out of this dead."

Nisman's concern came from the complicated, controversial nature of his work. He had led a long investigation into the 1994 bombing of the Asociación Mutual Israelita Argentina (AMIA) in Buenos Aires on July 18, 1994. The attack left 85 dead, making it the worst act of terrorism in Argentine history.

After previous investigations had been criticized for incompetence, in 2006, Nisman accused high\-level officials in Iran of orchestrating the attack and Lebanese group Hezbollah of carrying it out (Tehran has denied the accusations). By 2013, however, Argentina's government cut a deal with Iran to set up what it called a "truth commission" – a plan to investigate the bombing together, which critics called a whitewashing of Tehran's alleged involvement in the bombing.

Just last week, Nisman had accused Argentine President Cristina Fernández de Kirchner of secretly negotiating with Iran to avoid punishing those responsible. “The president and her foreign minister took the criminal decision to fabricate Iran’s innocence to sate Argentina’s commercial, political and geopolitical interests,” Nisman said, according to the Associated Press.

On Monday, Nisman was due to appear at a congressional hearing to further explain his accusations. He claimed to have evidence from wire taps that was damning for the government.

Firemen search for wounded after a bomb exploded at the Asociación Mutual Israelita Argentina (AMIA) in Buenos Aires on July 18, 1994, killing 85 and wounding about 300 others in the worst attack of its kind in the country's history. (Ali Burafi/AFP)

Instead, he was dead – his police protection discovered him locked inside his luxury condo in the Puerto Madero neighborhood of Buenos Aires with a .22-caliber handgun and a shell casing next to his body. There have been no reports of a suicide note, and his ex-wife has stated that he would not have killed himself.

Investigators have ruled out the possibility of a robbery, yet observers have picked up on strange yet inconclusive details – a lack of gunpowder on his hands, the presence of security minister Sergio Berni at the apartment after the crime – as evidence of something nefarious.

If Nisman did not kill himself, who did? The complicated nature of the case provides fodder for a wide variety of theories.

The Argentine government's motive

One theory goes that Nisman had evidence that Kirchner's government, which has faced economic isolation since its $100 billion default in 2001, made the 2013 deal with Iran in a bid to end its energy crisis. Tehran had been making a push in Latin America at the time, hoping to find a release for the economic pressure put on it by sanctions. The deal gave both parties diplomatic legitimacy.

Kirchner has been in office since 2007 and is not eligible for reelection in October 2015's general election. However, along with her late husband Nestor, she has led Argentina for 12 years and probably hoped to pick a successor. Nisman, a former ally, could well have provided a damaging blow.

In a lengthy Facebook message posted Monday, Kirchner criticized Nisman's handling of the AMIA investigation, saying that his allegations against her government were intended to "lie, disguise and confuse." The Argentine press has also linked Nisman's investigation to the downfall of Antonio Stiusso, a high-ranking intelligence officer who was dismissed by Kirchner a few weeks ago.

It may seem farfetched that the Argentine government would kill a critic in such an obvious way. But the strange circumstances of the case have led to a great deal of speculation, and the country has a history of political assassinations.

The Tehran link

Nisman's allegations could have been damning for Iran and Hezbollah too, prompting some speculation that his death could have been arranged by Tehran. "Did Iran Murder Argentina’s Crusading Prosecutor Alberto Nisman?" one headline from the Daily Beast asks, linking Nisman's death to a number of others suspected of being ordered by Iran.

There's no apparent evidence linking Iran or Hezbollah to Nisman's death, says Philip Smyth, a researcher at the University of Maryland who studies Shiite militant groups says, though it's certainly not outside the realm of possibility. "Iranian-backed groups and their own intelligence services ... can and have been pretty good practitioners of their 'art' (if one wishes to call it that)," Smyth writes in an e-mail. "Hezbollah's assassins and operatives are rather professional – depending on their areas of operation," he adds.

Nisman's death has led to intense speculation in Israel (the 1994 AMIA bombing was one of the worst attacks on Jews since the Holocaust). An article published Tuesday by the Jerusalem Post pointed out that Nisman's death came just hours after Israeli missiles killed a number of commanders from Iran and Hezbollah in the Golan Heights. "Iranian and Hezbollah media hinted that their killing would be avenged," Israeli journalist Yossi Melman wrote.

A corpse to discredit Kirchner?

On Twitter, Noga Tarnopolsky, a journalist of Argentine background who works in Israel, has said that no one she knows seems to have any doubt about who was behind Nisman's death, with all fingers pointing toward  Argentina's intelligence services, the Secretaría de Inteligencia.

However, in a string of tweets, she argued that Argentina's intelligence community is fractured, with one side supporting Kirchner and one side wanting to punish her. The latter may have had an incentive "to lay a corpse at Kirchner's feet," she explained.

Some government officials have pushed this theory, suggesting that former intelligence officials and the Clarín Group, a major Argentine media conglomerate often at odds with the government, might have somehow orchestrated Nisman's death. According to the New York Times, the Clarin Group has rejected any link, calling such ideas "conspiracy theories."

Whatever happened, the death of the 51-year-old father of two has deeply shocked Argentina and may well lead to wider reverberations.

On Twitter, Sergio Bergman, a rabbi and Argentinian lawmaker, called Nisman "victim 86 of the AMIA bombing," a terror attack no one has ever been punished for.