Reports in Argentina say a former top spy will give evidence today to the inquiry into the mysterious death of the prosecutor Alberto Nisman.
It comes as several thousand people demonstrated in Buenos Aires demanding justice in the case.
Reforms to the country’s intelligence services have been promised but campaigners suspect they won’t go far enough.
Human rights activist and Nobel Peace Prize winner Perez Esquivel was at the rally.
“The ‘dis-intelligence services’ have always been on the side of those in power and not the people. A deeper reform is needed, not just a makeover like they’re doing.”
Laura Ginsberg’s husband was killed in the 1994 bombing of a Jewish centre that Nisman was investigating.
She called for an end to “this pattern of impunity that’s gone on for 12 years under Kirchner governments. The case mustn’t be closed until it’s clarified”.
Nisman’s death, she added, highlighted such impunity.
Following the call by President Cristina Fernandez for the existing spy set-up to be disbanded, a Senate committee has been debating a bill to create a new federal intelligence agency.
But the opposition refused to take part, saying the process simply served government interests.
Conspiracy theories abound, more than two weeks after the prosecutor was found shot dead at his home.
Nisman had accused President Cristina Fernandez of a cover-up over the bombing.
The senior spy that reports say is to testify has been accused by the government of misleading the prosecutor.