The group of prosecutors that organized a massive march in Buenos Aires had called for a silent march to demand justice for their slain colleague, but the thousands who walked through driving rain to the city's iconic Plaza de Mayo today were anything but quiet.

A defiant mood gripped the crowd as the sound of thunder overhead competed with calls of "Justice for Nisman," purposeful clapping and nationalist chants.

Mostly comprised of the city's middle and upper classes, those marching represented a cross-section of citizens opposed to the populist government of embattled President Cristina Fernandez de Kirchner.

They had come to demand accountability for the unresolved death of special prosecutor Alberto Nisman, whose shooting on January 18 rocked the political establishment here and deepened the mystery of the unsolved 1994 bomb attack on the AMIA Jewish cultural center that left 85 people dead and hundreds injured.

In the center of the crush walked Nisman's ex-wife, Judge Sandra Arroyo Salgado, who had called for a politically neutral expression of outrage for Nisman's death amidst an increasingly partisan atmosphere.

"I don't have a political goal," Arroyo Salgado said in a televised speech on Friday, prior to the rally. "I don't back the government or the opposition. What I want is due process."

Unsolved shooting

Nisman, 51, was found dead in his Puerto Madero apartment just hours before he was due to deliver testimony regarding an alleged government operation aimed at covering up the 1994 bombing and absolving the Iranian suspects involved.

Fernandez and other close aides have been formally charged in what is alleged to be a conspiracy between Buenos Aires and Tehran motivated by trade.

The 289-page complaint alleges that Tehran would agree to provide the Kirchner administration with oil in exchange for grain, in a bid to ease both Argentina's chronic energy shortage and Iran's deprivation under Western sanctions for its disputed nuclear program.

The complaint also asserted that the Fernandez government asked Interpol to lift international arrest warrants on the Iranian suspects, a claim denied by former Interpol Secretary-General Ronald Noble.

Argentine Foreign Minister Hector Timmerman rejected the allegations, asserting that Argentina had no use for Iranian heavy crude and instead it needed refined oil until the country's vast hydrocarbon reserves at Vaca Muerta could be exploited.

Those taking part in Wednesday's march believed otherwise.

"This is a criminal government," one protester told DW. "We have no faith in what they say any more. Fernandez must face justice for the crimes she has committed."

'Political motives'

Government loyalists, however, denounced the rally as an "attempted soft coup" designed to force the president from office.

Among those in attendance were future presidential hopefuls, including the Renewal Front's Sergio Massa.

It was Massa's split from the ruling Front for Victory party last year that led to what may have been a catalyst for Nisman's shooting: the shake-up of the country's feared Intelligence Secretariat (SI) in December.

Fernandez was reportedly outraged that the intelligence service had failed to inform her that Massa would break ranks ahead of the Buenos Aires provincial elections last year.

The resulting restructure of the intelligence agency left veteran spymaster Jaime Stiusso out in the cold as he was replaced by a Fernandez loyalist.

Stiusso, a 40-year veteran of the intelligence service, is now a key person of interest in the shooting death of Nisman. Said to be one of the most powerful men in the country, he has been called to appear in court, although his whereabouts remain unknown.

Nisman reportedly had close ties with the former spy chief, and it was Stiusso's access to wire-tapped phone conversations that formed the basis of Nisman's legal argument that took aim at the Kirchner administration.

A labyrinthine case

Demonstrators bemoaned the layers of conspiracy, mismanagement and cover-up that have marked the AMIA case even prior to Nisman's unsolved death.

Numerous lines of investigation have been pursued and then dropped, including suspicions of Syrian involvement, or the collusion of anti-Semitic members of the Argentine security forces with "external actors."

This month, a judge and several police officials were charged with providing false information to investigators that would have placed Buenos Aires provincial police agents as suspects in the bombing.

Victims groups of the 1994 attack were divided on the march, with some denouncing the presence of people they said were "key to covering up the bombing in the first place."

The head of the Memoria Activa victims group, Diana Malamud, told local media that “both Nisman's complaint and his death are being exploited for means other than finding the truth” behind the 1994 attack.

Many at the rally said they were tired of intrigue and mystery surrounding the case.

"All we want is truth and justice," one protester said. "That is the value this government claims to uphold."