An Argentine prosecutor who died last year just days after accusing then-President Cristina Fernandez of covering up Iran's alleged role in the bombing of a Jewish center was apparently murdered, an official investigating the case said on Thursday.

Alberto Nisman was found shot dead in the bathroom of his Buenos Aires apartment 13 months ago. The case had been classified as a suicide, an idea Nisman's family and friends dismissed as absurd. Polls show most Argentines believe his death was a homicide.

"The evidence up to this point supports the hypothesis that Alberto Nisman was the victim of the crime of homicide," Ricardo Saenz, district attorney for the Buenos Aires Criminal Appeals Court, wrote in a recommendation that the case be handed over to federal authorities and pursued as a murder investigation.

It was the first time that a judicial authority had classified the death as a homicide. The move came amid a raft of changes made since President Mauricio Macri was inaugurated in December.

Macri pledged during the campaign to get to the bottom of the Nisman mystery and he promised justice when he met last month with Nisman's daughters, who are plaintiffs in the case.

When Nisman's body was discovered he was less than a day from a scheduled appearance in Congress to outline his accusation that Fernandez tried to cover up Iran's alleged role in the 1994 truck bombing of a Buenos Aires Jewish center.

Found on the floor, a pistol by his side and a bullet in his head, Nisman had been leading Argentina's probe into the bombing.

Fernandez said Nisman had been tricked by a former Argentine spy chief and his cronies into fabricating baseless allegations to destabilize her government. She theorized that the ex-intelligence officer then needed to silence him.

"They used him while he was alive and then they needed him dead," she said several days after Nisman died.

The attack on the AMIA center in Buenos Aires killed 85 people. Iran has repeatedly denied any link to the bombing and an Argentine judge tossed out Nisman's accusations against Fernandez as baseless.