Argentina's President Cristina Fernandez has made an about-face and says she is "convinced" the death of prosecutor Alberto Nisman, who had accused her of whitewashing a terrorist investigation, was not a suicide. In a letter published on social media sites, Fernandez said questions about Nisman's death "have been converted into certainty. The suicide [I'm convinced] was not a suicide." The 51-year-old Nisman was found slumped in the bathroom of his apartment late on Sunday with a bullet wound in his head. He was lying next to a .22-caliber handgun and a bullet casing. The death came days after Nisman gave a judge a 289-page report alleging Fernandez secretly reached a deal to prevent prosecution of former Iranian officials accused of involvement in the 1994 car bombing of Argentina's largest Jewish centre, an attack that killed 85 people and injured more than 200. His death has rocked Argentina, with polls saying a majority of people reject the idea that Nisman killed himself only hours before he was scheduled to detail his allegations before congress. Fernandez's letter contrasts with one she wrote on Monday in which she appeared to support the initial finding of suicide, and political analysts said her flip-flop could provoke further turmoil and cast doubt on the investigation's independence. "Most of the time, in the Western world, we would say, 'It's under investigation,'" said James Cooper, professor at California Western School of Law and an expert on legal reform in Latin America. "Now Cristina came out with this. All the rules are turned on their head." Fernandez's latest statements set off a round of questions and sharp criticism from the opposition leaders. In her letter, Fernandez dismissed Nisman's allegations of a cover-up and said he had been given false information about alleged Iranian spies from Antonio "Jaime" Stiusso, the former operations director of the Secretariat of Intelligence who recently had been replaced. She said Nisman had been caught up in internal power struggles in the intelligence community. Argentina's Foreign Minister Hector Timerman denied the government was behind his death. "Nobody wanted more Mr Nisman to live and to answer the questions than the president and myself," he told CNN.