An Argentine prosecutor was found dead just hours before giving what was expected to be damning testimony against President Cristina Kirchner. The body of Alberto Nisman, 51 - who had received threats after accusing the president of shielding Iranian suspects in the nation’s deadliest terror attack that killed 85 people - was found dead in his 13th-floor apartment in the upscale Puerto Madero waterfront neighbourhood of Buenos Aires. Officials have declared it a suicide, a statement likely to be scrutinised. “All signs point to suicide,” said Public Safety Secretary Sergio Berni, an assertion backed up by initial forensic findings. Federal prosecutor Viviana Fein said Nisman died of “a gunshot wound to the temple” and “there was no role of additional parties [in the death]". He was found in the bathroom, inside his locked apartment. However, there was no suicide note or witnesses, Fein added, calling for “caution”. The leader of one opposition party called it “an assassination”. Fein said the preliminary autopsy found “no intervention” of others in Nisman’s death. However, Fein said she would not rule out the possibility that Nisman was “induced” to suicide, adding that the gun was not his. “The firearm belonged to a collaborator of Nisman” who had given it to the prosecutor, Fein told Todo Noticias television channel. Several thousand protesters mobilised downtown in front of the presidential palace and Buenos Aires Cathedral, demanding an explanation for Nisman’s death. Clapping and shouting “killer” the demonstrators held banners reading “justice” and “killed for investigating”, as well as “Yo soy Nisman,” a take on the “Je Suis Charlie” slogan that appeared after Paris attacks that included the Charlie Hebdo satirical magazine. “I am here to seek justice for Nisman, so that we get to the truth about what happened to this man,” Carolina Arias, 31, said. According to the autopsy, Nisman had a bullet entry-wound on the right side of his head but there was no exit wound. His body was found inside the bathroom and blocking the door, and there were no signs of forced entry or robbery in the apartment, Fein said. Nisman, who had accused Kirchner of obstructing an investigation into a 1994 Jewish centre bombing, was due to testify at a congressional hearing on Monday to provide evidence of his claims. Since 2004 he had been investigating the van bombing of the Argentine Jewish Charities Federation, or AMIA, which left 85 people dead and 300 others wounded. He had been appointed that year by Fernandez’s late husband, then-president Nestor Kirchner, to revive the floundering investigation. The prosecutor had accused Iran of being behind the attack and said Cristina Kirchner hampered the inquiry to curry favour with the Islamic republic and gain access to its oil. Nisman was guarded by 10 federal police officers because he had received threats. Late on Sunday, agents alerted their superiors that he wasn’t answering phone calls, according to the Security Ministry statement. Authorities called Nisman’s mother and when she wasn’t able to open the door because a key was in the lock on the other side, a locksmith was called, the ministry said. A .22 caliber handgun and a shell casing were found next to Nisman’s body. Kirchner, who has denied Nisman's accusations, ordered the declassification of intelligence information Nisman had sought a week ago as part of his probe, apparently an attempt by the administration to show transparency and avoid any accusations of wrongdoing. In a letter on her official website,Kirchner lamented Nisman’s death, saying it generated “stupor and questions”. She initially used the word “suicide” in connection with his death but later put a question mark next to the word. In Uruguay, some 500 Argentines demonstrated in the beach resort city of Punta del Este, singing the Argentine national anthem and cutting off part of the town’s main promenade. Israel meanwhile expressed sorrow over Nisman’s death, praising him as a courageous jurist who “worked with great determination to expose the attack’s perpetrators and dispatchers”. Officials said a .22-calibre handgun was found beside Nisman’s body, which was discovered by his mother in the bathroom of his apartment after his security detail was unable to contact him. Nisman had also been expected to lodge accusations against Kirchner’s foreign minister Hector Timerman. Congresswoman Cornelia Schmidt-Liermann, interviewed before the preliminary autopsy finding, said she had planned to pick Nisman up Monday at his residence and accompany him for his testimony. “Everybody who had contact with him the last 24 hours says he was confident” about his testimony, she told The Associated Press . “There is no indication, under any circumstances, that he killed himself.” Schmidt-Liermann said Congress met Monday afternoon despite Nisman’s absence, and many members signed a declaration urging a full investigation into Nisman’s death and insisting that the investigation continue. Schmidt-Liermann and others who knew Nisman said he lived under constant threats on his life from Iranian agents and pressure from the Argentine government. Nisman had also accused former president Carlos Menem (1989-99) of helping obstruct the investigation into the bombing, which has never been solved. Since 2006, Argentine courts have demanded the extradition of eight Iranians, including former president Akbar Hashemi Rafsanjani, over the bombing. Argentina charges that Hezbollah, the Lebanese Shiite movement, carried out the attack under orders from Iran, which Tehran denies. Nisman had said that he had phone recordings that allegedly show the Kirchner government and Argentine authorities had bowed to Iranian demands after Tehran dangled lucrative commercial contracts. Nisman was supposed to present proof of his allegations that Kirchner and Timerman had a “plan of impunity” to “protect the Iranian fugitives.” He had also ordered the freezing of assets worth some US$23 million of Kirchner, Timerman and other officials. Opposition lawmaker Patricia Bullrich said she was shocked by Nisman’s death, calling it “a grave affront to the country’s institutions”. Bullrich said she had spoken to Nisman on the phone on Saturday on three occasions and he said that he had received several threats. Elisa Carrio, leader of the Civic Coalition, an opposition party, bluntly called Nisman’s death “an assassination”, saying she did not accept that it was a suicide. In 2013, Argentina’s Congress approved, at the request of the executive branch, an agreement with Tehran to form a truth commission to investigate the bombing, consisting of five members from neither Argentina nor Iran. The Jewish centre bombing came two years after an attack against the Israeli embassy in Buenos Aires that killed 29 people. Argentina’s Jewish community of about 300,000 people is the largest in Latin America.