Demonstrators in Buenos Aires hold images of the late prosecutor Alberto Nisman on March 18, 2015, during a rally demanding justice more than a month after his death. (Natacha Pisarenko/AP)

The fictional world of the late Argentine writer Jorge Luis Borges was a place of bookshelves that stretched to infinity, dreams within dreams and detective stories that led in ­circles.

Argentina for the past 14 months has been lost in a real-life labyrinth worthy of a Borges fable — ever since prosecutor Alberto Nisman was discovered dead in a pool of blood on his bathroom floor.

The body of Nisman, 51, was found the day before the prosecutor was expected to publicly accuse then-President Cristina Fernández de Kirchner of making a secret pact with Iran to gloss over Tehran’s possible role in the 1994 bombing of a Jewish community center in Buenos Aires. It was South America’s worst terrorist attack.

Investigators initially ruled Nisman’s death a suicide. Argentines took to the streets in protest.

As President Obama arrives in Buenos Aires on Tuesday for the first state visit by a U.S. president in 19 years, the unsolved mystery of Nisman’s death continues to hang over the country, casting a shadow far beyond Argentina’s borders.

“Everyone knows it was a homicide,” said Jorge Asís, a columnist and retired diplomat, “but no one can prove it.”

Nisman’s family and supporters have been pressing for a formal homicide investigation, and on Friday a federal tribunal in Buenos Aires heard new arguments seeking to elevate the case to a high-level homicide probe. The three-judge panel could accept those arguments or leave the case with lower courts, upholding the version of events that points to a suicide. A ruling is expected in the coming days.

The judge previously overseeing the case referred it to Argentina’s highest court after Antonio Stiuso, the country’s shadowy former intelligence chief, made a dramatic return from self-
imposed exile in the United States last month and testified that Nisman had been killed by a “group of people” with ties to former president Fernández de Kirchner. Stiuso, who worked closely with Nisman, offered no evidence for the claim, according to attorneys who have seen his sealed ­testimony.

New Argentine President Mauricio Macri, a centrist whose election in November ended 12 years of governance by Fernández de Kirchner and her late husband, Néstor Kirchner, has promised Argentines a thorough, impartial investigation to clear up once and for all how and why Nisman died. But the circumstances of the death are so murky that few here think the country will ever know what happened.

Nisman had spent more than a decade investigating the 1994 bomb attack that killed 85 people at the Argentine-Jewish community center known by the acronym AMIA.

Argentina initially blamed Hezbollah agents and Iran for the attack, and in 2004 Nisman was assigned to the case by then­President Néstor Kirchner, who said the previous investigation had been botched. Interpol Red Notice arrest warrants were issued for several top Iranian officials, essentially barring them from leaving their country, and Kirchner denounced Tehran at the United Nations and other international forums.

In 2007, Kirchner was succeeded by his wife, Cristina, just as relations with Iran were beginning to improve. She drew Argentina close to then-President Hugo Chávez’s Venezuela, which had friendly ties with Iran. Another close ally of Iran’s, Syrian ruler Bashar al-Assad, visited Buenos Aires for talks with the president in 2010.

[ Bashar al-Assad’s curious trip to Argentina]

It was then that Kirchner agreed to reset relations with Iran, a major market for Argentine grain. Nisman later alleged that her government had begun maneuvering to have the Interpol warrants lifted as part of an agreement she signed with Tehran in 2013 to form a “truth commission” to investigate the bombing.

Nisman objected to the accord, and his relationship with Fernández de Kirchner frayed.

[ Macri pulls out of Argentine-Iranian truth commission]

The death

On Jan. 19, 2015, Nisman was preparing to go before Argentina’s Congress to denounce Fernández de Kirchner in a report accusing her government of colluding with Iran to bury the investigation into the bombing.

According to the official version of events, Nisman that weekend dismissed the government security team assigned to protect him, then summoned his aide Diego Lagomarsino and asked to borrow a gun. Lagomarsino said he returned with the weapon to Nisman’s apartment in an upscale Buenos Aires district, then left.

Nisman subsequently died from a bullet to the head that had been fired from Lagomarsino’s .22-caliber Bersa pistol.

There was no sign of forced entry. No suicide note. Investigators swarmed the apartment, contaminating the crime scene, according to Nisman family attorneys. Nisman’s computer and cellphone appeared to have been altered.

Fernández de Kirchner initially called the death a suicide, then backed away from the claim. A month later, 400,000 protesters marched in silence through the rainy streets of Buenos Aires.

It was not until last month that a government prosecutor, Ricardo Sáenz, made the first official recommendation that Nisman’s death be investigated as a ­homicide.

The critical piece of evidence for Sáenz: Nisman had no gunshot residue on either hand. In addition, he had displayed no signs of depression. On the contrary, friends and relatives say, he had seemed eager and determined to deliver his report to Congress.

“As far as I’m concerned, he was murdered,” Sáenz said in an interview.

Sáenz, who has clashed publicly with Fernández de Kirchner in the past, said: “I won’t rule out that the former president will be called to testify.”

“She said it was a suicide, then later it was a homicide, so she should be asked what information she had,” he said. “I think she should be called to clarify what she knows.”

Supporters of Fernández de Kirchner accept that Nisman might have been murdered, but they suggest that his killing could have been part of a diabolical scheme to frame Fernández de Kirchner.

[Nisman’s ties to foreign intelligence]

The aide’s connection

Suspicion also falls on Lagomarsino, the aide hired by Nisman to help with his computer needs and whose fingerprints were strangely absent from the gun he said he lent to Nisman. Lagomarsino was the last person known to have seen the prosecutor alive, and his attorneys have fought the Nisman family’s attempt to elevate the case to a federal murder investigation.

In a bizarre twist, Lagomarsino is under investigation in a separate probe along with Nisman’s mother and sister, whose names appear on a U.S. bank account of Nisman’s that contains more than $666,000. Nisman failed to report the account, which is illegal for a prosecutor, and investigators say he also used his mother’s name to hide his ownership of three investment properties in Uruguay.

Stashing money and investments outside Argentina is nothing exceptional for someone with Nisman’s profile, prosecutors say. But tracing the payments in those accounts may be one of few ways to map out Nisman’s web of relationships and obtain new clues as to who might have wanted him dead.

This story has been updated to clarify that AMIA is an Argentine Jewish community center, not an Argentine-Israeli government initiative.

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