A special prosecutor who accused Argentine President Cristina Fernández de Kirchner of shielding Iranian suspects as part of a cover-up in the investigation of a deadly 1994 attack has been found shot dead, authorities said Monday.

Alberto Nisman, who was set to testify Monday in a congressional hearing about the bombing of a Jewish center — in which 85 people were killed — was found in the bathroom of his Buenos Aires apartment late Sunday, federal prosecutor Viviana Fein told Telam, Argentina's official news agency.

Hours later she told the press that an autopsy suggested that no other people were involved in his death. However, she said she would not rule out the possibility that he was "induced" to suicide, because the gun was not his.

"The firearm belonged to a collaborator of Nisman," Fein told Todo Noticias television channel. "He had had it a long time."

Nisman was appointed 10 years ago by Fernández's late husband — then-President Nestor Kirchner — to investigate the 1994 attack on the Argentine-Israeli Mutual Association in Buenos Aires.

Argentina has one of the largest Jewish communities outside of Israel, estimated at about 200,000, mostly in Buenos Aires.

In 2013, Argentina and Iran reached an agreement to investigate the attack, which remains unsolved. That year Nisman released an indictment accusing Iran and Hezbollah of organizing the blast. Iran denies any involvement.

Last week he accused Fernández and other senior Argentine officials of agreeing not to punish at least two former Iranian officials in the case. He asked a judge to call Fernández and others, including Foreign Minister Hector Timerman, for questioning.

"The president and her foreign minister took the criminal decision to fabricate Iran's innocence to sate Argentina's commercial, political and geopolitical interests," Nisman said last week.

Fernández has yet to comment on the allegations, but administration officials have called the prosecutor's allegations ludicrous.

A federal judge began the process of deciding whether to hear the complaint and whether anyone should be summoned for questioning.

Opposition Congresswoman Patricia Bullrich told local news media that Nisman told her he received threats after accusing the president.

Late Sunday, federal police agents in charge of his protection alerted their superiors that he wasn't answering phone calls, according to a statement from the Health Ministry. When he also didn't answer the door, they decided to alert family members, according to the statement.

When his mother wasn't able to open the door because a key was in the lock on the other side, a locksmith was called to open it, the ministry said. A .22 caliber handgun and a shell casing were found next to his body.

Within hours after news of Nisman's death spread, a well-known group called Indignant Argentines called for demonstrations later Monday in several areas of Buenos Aires.

"Nisman died, but his denouncement does not," Sergio Bergman, a prominent rabbi in Buenos Aires, posted on Twitter. "Our sorrow and condemnation will result in more memory, truth and justice!"

Al Jazeera and wire services