A Holocaust expert has been named to take over as judge in the politically sensitive case of a 1994 Jewish centre bombing that has shaken Argentina since the lead prosecutor's mysterious death.
Daniel Rafecas's appointment comes weeks after prosecutor Alberto Nisman, who had drafted an arrest warrant for President Cristina Kirchner, was found dead in his apartment with a gunshot wound to the head.
It remains unclear whether Nisman, who died last month, committed suicide or was murdered.
Rafecas, a human rights expert, has authored studies on the Holocaust that earned him awards from several Argentine Jewish groups.
He is also known for trying military officers for abuses committed during the South American country's 1976-1983 dictatorship.
The case has become a political hot potato since Nisman, 51, died on the eve of a congressional hearing at which he was expected to accuse Kirchner of covering up Iranian officials' involvement in the bombing that killed 85 people and left 300 wounded.
It was the worst attack on Argentine soil in the country's modern history.
The federal authority for criminal courts appointed Rafecas to take on the investigation after other judges had asked to recuse themselves from the case, which has gripped Argentina.
Around 2,000 people meanwhile rallied behind a banner that read "enough impunity" as they marched through the capital Buenos Aires, calling for answers.
"I think we will end up with the truth," said Argentine Nobel Peace Prize laureate Adolfo Perez Esquivel, who marched at the head of the crowd, calling for an investigation by an independent commission.
According to polls, some 70 percent of the population believes they will never know the truth behind Nisman's death.
Nisman was named in 2006 to reopen the case after the initial investigation ended with no convictions.
He accused Iran of ordering the attack via the Lebanon's group Hezbollah, and requested arrest warrants for five Iranian officials, including former president Akbar Hashemi Rafsanjani.
On January 14, four days before he was found dead, Nisman filed a 300-page report accusing Kirchner, foreign minister Hector Timerman and another senior official of trying to shield the Iranian suspects in exchange for oil.
Nisman's death is being investigated by prosecutor Viviana Fein, who caused further controversy by initially denying that Nisman had drafted an arrest warrant for Kirchner.
Fein later said such a warrant had in fact been found in Nisman's apartment, denying she had succumbed to government pressure to cover it up.
In a bid to forestall further controversy, Fein said on Wednesday she was cancelling her plans to go on vacation on February 18, which had drawn criticism from some, including the government.
"I've never been pressured, I'm not afraid," she told a press conference.