A top Argentine prosecutor is telling the country's criminal court of appeals that he believes his late colleague Alberto Nisman was killed and didn't take his own life.

Ricardo Saenz's opinion marks the first time that a judicial official has called Nisman's death a homicide.

The opinion presented Thursday was sought in an appeal by Nisman's ex-wife, who is pushing for a federal court investigation.

Nisman was found dead in his apartment on Jan. 18, 2015. Days earlier, he had accused President Cristina Fernandez of helping Iranian officials cover up Iran's alleged role in the 1994 bombing of a Jewish community center. The case against Fernandez was later thrown out.

The mysterious death rocked Argentina, but has not been solved.