Argentina’s President Cristina Fernández de Kirchner made a dramatic U-turn on Thursday when she said she was certain that prosecutor Alberto Nisman was murdered although she had previously insisted he had taken his own life.

In a rambling 2800-word letter published on her social media accounts on Thursday, Fernández described Nisman’s death as “the suicide that (I am convinced) was not a suicide.” Nisman’s body was found late Sunday night, only a few hours before he was about to present evidence in Congress that he claimed showed Fernández had negotiated secretly to shield five Iranian officials from charges they had masterminded a bombing in Buenos Aires that resulted in 85 deaths in 1994.

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The president’s first claim that Nisman had committed suicide (“What led (Nisman) to take the terrible decision of ending his own life?” she asked on Monday) fell apart in the face of mounting evidence against the suicide theory.

Her government’s first claim that the back door to Nisman’s apartment was locked from the inside was disproved when investigators revealed that the door was not locked and there was also a third entrance to his home. Investigators could not find any gunpowder residue on Nisman’s hands, which would have suggested he had fired a gun.

On top of that, a long list of friends, journalists and even his personal trainer came forward to say that Nisman was eagerly looking forward to appearing before the Argentine Congress on Jan. 19. Nisman had even set up a series of meetings and interviews for the following week.

Both his former wife, 45-year-old Judge Sara Arroyo Salgado, and his mother, 73-year-old Sara Garfunkel, who found his body on Sunday, came out firmly against the suicide hypothesis. “All kinds of things have been said about my son,” Garfunkel said in a brief phone call with the daily Clarín Thursday, answering with a “No” when asked if she thought he had taken his own life.

Nisman’s planned presentation of the evidence to Congress on Monday would have damaged Fernández’s already-beleaguered administration. She is in the last year of a two-term presidency that has been badly shaken by crippling inflation, recession and charges of corruption involving her highest officials.

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The president has not been seen in public since before Christmas, when she sprained an ankle in an accident.

Nisman’s breakthrough in the bombing case came in 2007 when he was able to provide enough evidence for Interpol to issue international warrants for the arrest of the Iranians he identified as his main suspects.

His friends say he felt he was on the verge of a similar breakthrough. “I had seen him in person on Wednesday,” says Waldo Wolff, vice-president of DAIA, the most important Jewish community association in Argentina. “And I spoke to him on the phone on Saturday night after he sent me a photo via Whatsapp of his desk covered with the papers of the presentation he was preparing for Congress on Monday. He seemed well, his usual extroverted self.”

A poll this week showed that 70% of people in Argentina believe Nisman was murdered, while only 12% agree with the government’s hypothesis that he took his own life. The survey by the Ipsos research firm also revealed that 82% believed that Nisman’s charges that President Fernández was involved in secret deals with the accused Iranians are “credible.”

“Just in case, so you know, I have no plan to commit suicide,” says journalist Nicolás Wiñazki, who was in constant communication with Nisman in the days before his death. “Nobody believes the government,” Wiñazki says. “He was optimistic and looking forward to appearing before Congress, he was answering my messages with positive emoticons, thumbs-up and smileys up till Saturday. Then on Sunday he stopped answering.”

The same skepticism was expressed by Nisman’s former wife and mother of his two daughters, Judge Sandra Arroyo Salgado, who appeared in court briefly two days ago. “I don’t believe it was suicide,” Arroyo Salgado said to journalists on the sidewalk outside the courtroom.

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Nisman’s aim of bringing the suspects to justice was delayed in 2013, when Argentina’s Foreign Minister Héctor Timerman flew to Ethiopia to sign a surprise agreement with Iranian foreign minister Ali Akbar Salehi. The document established a binational “truth commission” to investigate the bombing and agreed to inform Interpol that the two countries were working together to solve the case.

The unexpected deal with Iran was met with protest at home, not least because it seemed to dash whatever hopes remained of bringing the main suspects to trial in Buenos Aires. “It was unbelievable,” says Wolff. “Signing a pact with a country accused of the worst terrorist attack ever in Argentina.”

What Nisman afterwards claimed he discovered was an attempt by Fernández to secure a secret deal trade deal with Iran in tandem with the public agreement. In a 300-page document presented in court last Wednesday, Nisman detailed secret talks between emissaries of Fernández, who communicated through a go-between in Buenos Aires, with Mohsen Rabbani, Nisman’s main suspect. The Argentine government wanted to obtain badly-needed oil from Iran to help Argentina out in exchange for the lifting of the Interpol arrest warrants, Nisman alleged.

Nisman’s evidence, including the recording of the conversations between Iranian and Argentinian representatives, are now in the the custody of Judge Ariel Lijo. He is expected to decide next month if Nisman’s evidence is enough to call Fernández in for interrogation.

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