An Argentine prosecutor was murdered days after accusing the country’s former president of hiding details of Iran’s involvement in a Jewish community centre bombing, a judge ruled on Tuesday.

Alberto Nisman was found dead nearly three years ago after accusing President Cristina Fernández de Kirchner of working to clear the Tehran regime of responsibility in an investigation into the 1994 attack.

“Nisman’s death could not have been a suicide,” federal judge Julian Ercolini said in a 656-page ruling.

The findings concluded there was adequate evidence that the shot to the head that killed the prosecutor was not fired by Mr Nisman himself. The decision was the first in which a judge has called the case a murder.

The ruling also charged Diego Lagomarsino, one of Mr Nisman’s employees, as an accessory to murder.

Mr Lagomarsino accepted lending Nisman the gun that killed him on the day before he was due to make his allegations against Ms Kirchner in Argentina’s parliament, but claimed his employer had asked for the gun to protect himself and his family.

Nisman was found dead in January 2015 days after alleging that President Fernández had covered up Tehran’s part in the attack, when a suicide bomber detonated an explosive-laden Renault van in front of the Buenos Aires headquarters of the Argentine Israelite Mutual Association.

It caused a building collapse that left 85 people dead and 300 injured.

Nisman had spent the last decade of his life investigating the attack after being appointed in 2004 by Néstor Kirchner, Ms Fernández’s husband and predecessor as president.

The appointment had been praised as a breakthrough after bungled and corrupt attempts to prosecute the case.

Nisman formally accused the Iranian Government of masterminding the attack and carrying it out through local Hezbollah agents.

He also accused Ms Fernández of secretly working to clear Iran of responsibility for the bombing as part of a plan to normalise ties and seal a 2013 grains-for-oil deal between the two countries.

Ms Fernández, a serving senator, was indicted this month for treason as a result of the claims.

Her indictment was criticised by the former Interpol head and human rights groups. Iran denies any connection to the attack.

Argentine authorities have so far only announced that DNA belonging to two others was found in the bathroom where Nisman was discovered dead.

Informally however, the principal suspects are believed to be warring factions in the Argentine intelligence services and Iranian Government, Haaretz reported.