An Argentine prosecutor who had accused the government of covering up alleged Iranian involvement in the 1994 bombing of a Buenos Aires Jewish center was found shot dead in his home on Sunday, the day before he was to testify over his claims.

In a case that has rattled Argentina, Alberto Nisman went public on Wednesday with a report claiming that President Cristina Fernández de Kirchner had secretly established a back channel with a group of Iranians suspected of carrying out the attack that killed 85 people — the deadliest bombing in the country's history.

The 300-page report on his investigation of the case accused Fernández de Kirchner and Foreign Minister Héctor Timerman of colluding to have the suspects cleared in order to smooth the way for a trade deal that would secure sorely needed Iranian oil in exchange for Argentine grain.

The report demands that the pair be questioned "for being authors and accomplices of an aggravated cover-up and obstruction of justice regarding the Iranians accused of the AMIA (Israeli-Argentine Mutual Association) terrorist attack."

On Sunday night, Nisman's body was found in the bathroom of his apartment in the Buenos Aires district of Puerto Madero with a 22-caliber handgun and bullet casing by its side, according to the Argentine Security Ministry. The daily Clarin said he had been shot in the head.

The ministry said the body was discovered by Nisman's mother, who had been alerted by the prosecutor's security detail that he was not answering his phone or door, and had not collected the Sunday newspapers from his doorstep. She had reportedly visited the apartment, where she called a locksmith to open the door after finding it had been locked from the inside.

"Everything indicates it was a suicide," Secretary of National Security Sergio Berni told local television. "We have to see if gunpowder is found on his hands."

However, investigating prosecutor Viviane Fein said that no suicide note had been left in the apartment. The state of his apartment ruled out burglary as a motive, she added. "It was in perfect condition, there was no mess, nothing was missing." An autopsy was underway on Monday.

But the timing of the death of the 51-year-old prosecutor, who was due to formally present his accusations in a closed-door parliamentary committee hearing today, has stirred suspicions.

"I could end up dead because of this," Nisman told Clarin last week. But speaking to VICE News ahead of the hearing, Nisman said he was "very calm."

"I know that I'm accusing President Cristina Kirchner, it's not a minor question," he said. "I keep the telephone switched off most of the time but I'm preparing myself. I've spoken already, now is the time for the evidence to speak for itself."

Nisman said the government had a team of people working to discredit his investigation, but reiterated: "The president, Cristina Kirchner, and her foreign minister, Héctor Timerman, headed a criminal plan which involved distancing Iran from responsibility for the attack on the AMIA, in which 85 people died, in exchange for doing business with oil and grain."

The unresolved case of the bombing has long been mired in claims of cover-ups and official incompetence, and remains an open sore in the country, which is home to Latin America's largest Jewish community. Late president Nestor Kirchner — who was Cristina Kirchner husband — once denounced it as a "national disgrace," and Pope Francis, formerly the archbishop of Buenos Aires, has even intervened to demand justice for the victims.

Argentine prosecutors have frequently accused Iran of sponsoring the attack — an allegation has consistently been denied by Iran's leaders — and in 2006 Nisman formally charged the country's government and Lebanese paramilitary group Hezbollah, calling for the arrest of former president Hashemi Rafsanjani and seven others. In 2007 Interpol issued arrest warrants for five Iranians — among them high-ranking members of the current government — and Imad Mughniyeh, Hezbollah's now deceased former operations chief.

In 2013 Fernández de Kirchner — who by then, along with other Latin American leftist governments, had struck up close political ties with the Iranian leadership — sought to establish a "truth commission" on the bombing in cooperation with the Islamic Republic.

But the initiative was criticized as a potential whitewash and was eventually struck down by an Argentine court.

Nisman's report accused the Kirchner government of operating a "clandestine" communications channel with Iran with "illicit objectives."

The report stated that the president wanted to bring Argentina closer to Iran, "establishing trade relations to mitigate Argentina's severe energy crisis through an exchange of oil for grain."

That was not considered viable while the issue of the bombing still remained, the report said. In order to "clear the obstacle," Fernández de Kirchner "ordered a diversion of the investigation, abandoning years of a legitimate demand of justice, and sought to free the Iranians accused in the case from all suspicions, contradicting their proven ties with the attack. She decided to fabricate the innocence of Iran."

Nisman said he had recordings of phone conversations between Iranian officials and Argentine mediators substantiating his claim of an agreement between Buenos Aires and Tehran to resolve the bombing case and move forward with the trade deal.

Argentine Cabinet Chief Jorge Capitanich immediately dismissed Nisman's allegations as "crazy, absurd, illogical, irrational, ridiculous, unconstitutional." The judge overseeing the bombing case criticized the prosecutor for "an investigation without judicial control" and suggested that his findings were flawed, Reuters reported.

The claims, and Nisman's death, will energize Fernández de Kirchner's critics, who have long painted her as a power-obsessed and corrupt authoritarian running a personal fiefdom from the Casa Rosada.

In a trenchant op-ed, the_Times of Israel_asked "Who will obtain justice for Alberto Nisman?," insisting that "decent people should be appalled" by his death.

"I find it very difficult to believe that Nisman killed himself. The man kills himself before testifying? Come on guys…" Jorge Lanata, a leading Argentine journalist and frequent critic of the government, told local radio.

Radio host and writer Alfredo Leuco said that even if Nisman had committed suicide, it was "a political death" resulting from the explosive nature of his claims. Whether suicide or murder, he added, "Nisman died because of the report he made."

Additional reporting by Gaston Cavanagh