Argentina suspects rogue agents from its own intelligence services were behind the death of a state prosecutor investigating the deadly 1994 bombing of a Jewish community center in Buenos Aires.
Alberto Nisman was found dead in his apartment late on Sunday, a gunshot wound to his head and a 22 caliber pistol by his side along with a single shell casing.
He had been scheduled to appear before Congress on Monday to answer questions about his allegation that President Cristina Fernandez conspired to derail his investigation of the attack.
His death and a blizzard of conspiracy theories around it have rocked Argentina.
The government says Nisman's allegations and his death were linked to a power struggle at Argentina's intelligence agency and agents who had recently been fired.
It says they deliberately misled Nisman and may have had a hand in writing parts of his 350-page complaint.
"When he was alive they needed him to present the charges against the president. Then, undoubtedly, it was useful to have him dead," the president's chief of staff, Anibal Fernandez, said on Friday.
Argentine courts have accused a group of Iranians of planting the 1994 bomb, which killed 85 people.