On Monday night, Argentina’s president, Cristina Fernández de Kirchner, took the bold step of announcing a plan to dissolve the country’s Intelligence Secretariat and send to congress a draft bill for the “reform of Argentina’s intelligence service” in the wake of the death of prosecutor Alberto Nisman nine days ago.

A possible explanation for Nisman’s death, which came only days after he announced charges that aimed to put Fernández on trial for an alleged conspiracy with Iran, seems to be hidden inside a complex saga of mind-boggling intrigue involving the intelligence agency she now intends to reform.

Created as the Information Division (División Informaciones) by Argentina’s strongman General Juan Perón in 1946, the service’s first task was to arrange the postwar transport of Nazi war criminals to Argentina, some of whom then went on to serve in Perón’s intelligence agency.

Since then, the service has changed its name a number of times, its latest incarnation being the Intelligence Secretariat, better known by its Spanish-language acronym SI. Under Fernández, Argentina’s secret service is alleged to have been involved in domestic spying on a scale rivalling that in Eastern European nations before the fall of the Berlin wall.

Nisman’s connection at the SI was Antonio, aka “Jaime” Stiuso, an enigmatic figure who for years reputedly ran a vast eavesdropping network that made him the most feared man in Argentina.

Few details about the man are in the public domain. He is a 61-year-old communications expert who joined the service in 1972 at 18 years of age. He has three daughters (for whom he reportedly sought security protection from a Buenos Aires court recently) and is reputedly extremely charming. “He’s charismatic, very relaxed, he laughs a lot,” says Rodis Recalt, a journalist from Noticias magazine who interviewed him last month. “After months of tracking him, he called me. I never saw him face to face.”

Under Férnandez in recent years, and under Néstor Kirchner, the president’s now-deceased husband and predecessor, Stiuso’s power is alleged to have grown exponentially, thanks to the extensive wiretapping services on political opponents that he allegedly carried out for the Kirchners.

“But last October, when Fernández found out through military intelligence that Nisman was preparing charges against her for an alleged cover-up of Iran’s role in the bombing, she became understandably furious that Stiuso had not alerted her,” an intelligence source told the Guardian.

By late December, when she began to suspect that it was actually Stiuso who had poisoned Nisman against her, she fired Stiuso and began preparing to dismiss Nisman as well. “She was doubting between replacing Nisman completely, or appointing two assistant prosecutors by his side to neutralise him,” the source maintains.

The president’s alleged fury was fuelled by the extensive use of wiretaps provided by Stiuso that Nisman made in his 300-page accusation against her.

In an long statement posted to her website last week, Fernández seemed to make the case that Nisman’s accusation was actually written by Stiuso, and that Nisman was then killed by the same people who convinced him to present the charges. “They used him alive and then they needed him dead,” Fernández wrote. “As sad and as terrible as that.”

Former president Kirchner introduced Nisman to Stiuso 11 years ago, when Kirchner put the prosecutor in charge of solving the 1994 bombing of the Amia Jewish community centre in Buenos Aires, which killed 85 people, the deadliest terrorist attack in Latin America. “The two developed a father-son relationship,” says the intelligence source, who knew both men well.

Only the security cameras on the front gate and an Argentinian flag draped from a white metal pole above the entrance indicate the location of the Judicial Observations Department on Avenida de los Incas 3834, a six-storey redbrick building in the upscale neighbourhood of Belgrano. An endless series of press articles and books allege, and at least one court raid has proven, that housed inside are a vast array of computers and recorders continually monitoring the activity of Argentina’s politicians, judges, prosecutors and journalists. Court-ordered wiretaps are also carried out there, since by law only the SI is permitted to intercept calls in Argentina.

Nisman made extensive use of the powerful eavesdropping capabilities of the facility while investigating the Amia blast. It was while poring over calls between Argentina and Iran that Nisman says he discovered the secret offer by Argentina’s government to shield Iranian officials from his arrest warrants, in return for Iranian oil. The calls were made to Iranian offical Moshen Rabbani in the city of Qom, who, as the former Iranian cultural attache in Buenos Aires at the time of the bombing, speaks perfect Spanish, the language used in all the transcribed calls.

Stiuso’s name was known to only a select few until 2004, when justice minister Gustavo Beliz, a politician with a reputation for honesty in a political arena widely considered to be mired in corruption, unmasked him. Beliz displayed a blurry photo of Stiuso on television and accused him of having mounted “a kind of Gestapo” to coerce politicians and journalists to follow the bidding of his political masters. Far from being rewarded for his courage, the minister was fired by Kirchner.

Beliz went into self-imposed exile in the United States and Uruguay, unable to return to public office. His withdrawal into silence is considered a testament to Stiuso’s far-reaching secret network.

But not everybody has such a negative vision of the man who reputedly pulled the secret strings of power in Argentina. “You should have seen how well received he was at the CIA and the Mossad,” says another intelligence source who worked closely with Nisman and Stiuso on the Amia case.

The two men became convinced, partly on the basis of intelligence provided by the United States and Israel, that Iran had been behind the blast. The biggest advance in the case came in 2007, when Interpol agreed to issue international “Red Notices” for the arrest of their five main Iranian suspects, Rabbani chief among them.

But when Argentina and Iran, as a result of the alleged secret negotiations Nisman uncovered, signed a public memorandum in 2013 to set up a joint “Truth Commission” to investigate the blast, effecitvely killing Nisman’s investigation, Stiuso and Nisman became disenchanted with Fernández. The slowly widening rift could explain Nisman’s decision to press charges against her, perhaps with Stiuso’s surrport, as Fernández seems to feel.

“Stiuso is an intelligence officer who follows commands to the letter,” says the intelligence source who worked on the Amia case. “But he was not prepared to betray his geopolitical alliance and put in jeopardy the great prestige he enjoyed with the western intelligence services.”

From 2013 onwards, the sources agree, Stiuso’s disenchamntment with Fernández led him to feed information to the courts and to journalists related to some of the numerous cases of corruption that have made headlines in Argentina in the last two years.

According to one of these sources, Stiuso has left Argentina for the United States. “He called me from the US a few days ago,” the source says. “He told me he was sickened by what is happening at the intelligence service, particularly by the firing of his 20 closest collaborators.”

In the face of the failed memorandum of understanding with Iran and the fact the “Red Notices” from Interpol are still standing, at least one former secret service chief has worries that extend far beyond the Nisman case.

“The purge of the service’s best anti-terrorist experts and the failure of the agrreement with Iran has left Argentina open to another Amia-style bombing,” says former Intelligence Secretariat chief Miguel Ángel Toma, who knew Stiuso and is also a firm believer that Iran had a hand in the bombing. “We managed to find even the exact date and hour at which the decision to bomb the Amia was taken in Qom,” Toma says. “I am extremely worried.”