T ens of thousands of Argentines marched through the capital Buenos Aires demanding answers over the mysterious death of prosecutor Alberto Nisman.
The protest came exactly a month after he was found in his bathroom with a bullet in his right temple.
In a case that poses a strong challenges to President Cristina Fernandez, marchers waved Argentine flags and carried white signs with black letters that read "Justice!" and "Truth!"
Many also carried umbrellas to repel a burst of summer rain.
Blanca Perez, 81, said she believed Mr Nisman had been murdered and the government needed to account for what happened.
"If we don't have justice, we won't have liberty," she said. "The government has lost control of the situation."
Organised by several prosecutors, protesters walked from Congress to Plaza de Mayo in central Buenos Aires.
Upon arriving at their destination, thousands stayed for more than an hour, chanting "Argentina!" and demanding action by the government.
The 51-year-old prosecutor was found in a pool of blood the day before he was to detail to Congress his explosive accusations that Ms Fernandez and senior government officials orchestrated a secret deal with Iran to shield Iranian officials allegedly responsible for the 1994 bombing that killed 85 people at a Jewish community centre in Argentina's capital.
Ms Fernandez has denied the allegations, but her administration has struggled to confront the growing political crisis.
The president initially suggested Mr Nisman had killed himself, then did an about-face a few days later, saying she suspected he had been killed.
The authorities now say they are investigating the possibility of suicide or homicide.
In the lead up to the march, the main opposition parties said they planned to participate, making it a hotly contested political issue and adding to intensifying rhetoric from the government.
Ms Fernandez has suggested Mr Nisman was killed by rogue counter-intelligence agents and has cast suspicions on Antonio "Jaime" Stiuso, who reportedly oversaw a vast wire-tapping operation before being removed by the president in December.
Mr Stiuso, who had worked with Mr Nisman on his investigation, provided testimony yesterday, according to the office of Viviana Fein, the lead investigator in the prosecutor's death.
Ms Fernandez and other administration officials also have suggested that the US and Israel have meddled with Argentina, but have not provided details.
In a speech at nuclear power plant yesterday, Ms Fernandez referred to letters that foreign minister Hector Timerman sent on Tuesday to his counterparts in the US and Israel.
Mr Timerman said the two countries should not get involved in Argentina's affairs, but did not provide specifics.
"Some people wanted to play dumb and look the other way," Ms Fernandez said of the accusations. "I urge all compatriots to read every paragraph of those letters."
She cast the apparent friction as a battle of economic interests and attempts by other countries to keep Argentina down.
"In reality, they prefer an Argentina without a nuclear plan, an Argentina that does not develop scientifically, an Argentina with low salaries and cheap labour," she said.