Buenos Aires (AFP) - An Argentine prosecutor found dead shortly before he was about to make explosive allegations about President Cristina Kirchner took a bullet point-blank to his forehead, justice officials said Saturday.

Authorities said Diego Lagomarsino, a computer expert and colleague who said he had brought prosecutor Alberto Nisman a handgun Saturday night at his request, has been barred from leaving Argentina.

Nisman was found dead with a bullet to the head in his Buenos Aires home on Sunday, just before he was set to go before a congressional hearing to accuse Kirchner and Foreign Minister Hector Timerman of shielding Iranian officials implicated in the 1994 bombing of a Jewish community center that killed 85 people.

It was Argentina's worst terror attack in modern history. It has never gone to trial fully. Several pretrials were cancelled amid serious irregularities involving judges and Argentine intelligence staff.

Investigators, who initially said Nisman appeared to have committed suicide, have not ruled out homicide or "induced suicide."

Kirchner, meanwhile, has said she believes the 51-year-old was murdered in a plot to implicate her government in a coverup.

Prosecutor Viviana Fein, who is leading the investigation, said investigators were waiting for ballistics analysis, including a DNA comparison, and to see whether the bullet taken from the body matches the .22-caliber weapon found at the scene.

Fein later told local television that the shot was fired "from a distance no greater than a centimeter" while reiterating her contention that there was no evidence third parties took part in the actual shooting itself.

"We are still awaiting the toxicological and tissue testing, which can take a bit longer," she added.

Before his demise, Nisman had filed a 280-page complaint charging that Kirchner had issued an "express directive" to shield a group of Iranian suspects in the 1994 bombing.

Nisman contended that the government had agreed to swap grain for oil with Tehran in exchange for withdrawing "red notices" to Interpol seeking the arrests of the former and current Iranian officials accused in the unsolved case.

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Since 2006, Argentine courts have demanded the extradition of eight Iranians, including former president Akbar Hashemi Rafsanjani, former defense minister Ahmad Vahidi and Iran's former cultural attache in Buenos Aires, Mohsen Rabbani, for the bombing.

But in 2013, Kirchner signed a memorandum of understanding with Tehran agreeing to set up a "truth commission" to investigate the bombing and allowing Argentine prosecutors to question the suspects in Iran.

The rapprochement was vehemently opposed at the time by Jewish community leaders, who charged it was "unconstitutional."

Argentina's Jewish community is Latin America's largest.