Authorities in Argentina say a special prosecutor who had accused President Cristina Fernandez of ordering impunity for Iranian suspects in the South American country's worst terrorist attack has been fatally shot.

Alberto Nisman, who was set to testify Monday in a closed-door hearing, was found in the bathroom of his Buenos Aires apartment late Sunday, federal prosecutor Viviana Fein told Telam, Argentina's official news agency.

Nisman had been appointed 10 years ago by the president's late husband, then President Nestor Kirchner, to investigate the 1994 bombing of the Argentine-Israeli Mutual Association in Buenos Aires, which killed 85 people and injured more than 200. In 2013, Argentina and Iran reached an agreement to investigate the attack, which remains unsolved.