Private forensic tests on the body of Alberto Nisman, the prosecutor who was investigating the circumstances surrounding the 1994 bombing of a Buenos Aires synagogue, indicate he was murdered.

His former wife, judge Sandra Arroyo Salgado, hired a private team to analyse the autopsy results and run additional tests.

Nisman was found lying inside his apartment, with a .22 calibre handgun by his side, on the eve of a testimony to Congress during which he was expected to accuse President Cristina Fernández de Kirchner, her foreign minister and other top officials of shielding Iranian officials who allegedly masterminded the bombing.

The mysterious circumstances surrounding his death on 18 January have unleashed a series of conspiracy theories.

While she has not given details of the findings to journalists, Arroyo Salgado deposited the forensic evidence behind her murder allegations at the state prosecutors' office in Buenos Aires.

Arroyo Salgado has claimed she does not believe an initial finding that he killed himself, telling a news conference: "Nisman didn't have an accident. He didn't commit suicide. They murdered him."

Argentine authorities are yet to release the full results of the autopsy, and the very few details made public so far have suggested suicide.

However the lead investigator into Nisman's death said she could not categorically say if he shot himself in the head or was killed.

Viviana Fein, the state prosecutor investigating Nisman's death, said she would study the evidence put forward by Arroyo Salgado's team.

"Up until now ... there has been nothing which allows me to say categorically whether this was a suicide or homicide. Nothing," Fein told the state-run National Radio.

This scandal has plunged President Kirchner's government into power during her last year in office.

While Kirchner has said that she does not believe that prosecutor Nisman committed suicide, the president has branded as "absurd" Nisman's accusation that she sought to whitewash his investigation into the bombing of the AMIA Jewish community center 21 years ago.