More than a dozen people have been arrested in Argentina after copies of notebooks were found detailing what seem to be illicit political payments.
They were kept by Oscar Centeno, who was employed as a driver by a public works official and describe delivering bags of cash.
The notebooks cover from 2003 to 2015, when Cristina Fernández and her late husband Néstor Kirchner were president.
Ms Fernández is yet to comment on the latest allegations.
Since President Mauricio Macri came to power in December 2015, dozens of officials from the previous administration have been linked to various corruption charges.
Ms Fernández has been called to testify on alleged payments during her time in office. She has previously said she is being politically persecuted by the current government, who want to distract people from the country's economic problems.
Oscar Centeno kept his notebooks when he was driver to Roberto Baratta, a high-level employee in the planning ministry, according to Argentine media.
Mr Centeno wrote down the times, value and even the weight of the bags of money he said he delivered as he drove around Buenos Aires.
He also listed the addresses he visited, and various other details, such as how often his boss went to the gym.
Eight of his notebooks were passed to La Nación newspaper earlier this year and its journalists worked on a story secretly for months before passing them on to judicial authorities.
The newspapers published its story on Wednesday amid the wave of arrests.
Reporters estimate that the payments total around US$56m (£43m), but Judge Claudio Bonadio says the corruption network could reached up to US$160m.
Mr Centeno has been arrested and is co-operating with investigators, but various business leaders who were also held have refused to testify, according to La Nación.
They include Javier Sánchez Caballero, the ex-CEO of construction company Iecsa, and Gerardo Ferreyra and Jorge Guillermo Neira, vice-presidents of Electroingeniería, which has been working on a high-profile hydroelectric project in Patagonia.
The former president of the Argentine Chamber of Construction, Carlos Wagner, was also arrested on Thursday.