Investigative website Mediapart has relentlessly published articles implicating Sarkozy and members of his inner circle.
Police are investigating Sarkozy's implication in the case, following claims he received millions of euros to fund his 2007 election campaign from the Libyan regime.
Former interior minister Brice Hortefeux was also questioned by police.
“Since 2011 we at Mediapart have obtained documentary evidence and spoken to people involved which confirm this illicit financing,” says Karl Laske, a Mediapart journalist who has been investigating the story for the past seven years.
“In 2013 police began an investigation using our evidence.”
Investigators have evidence of five million euros being brought to Sarkozy in suitcases, but they are also examining the claim that Kadhafi promised to give Sarkozy a total of 50 million euros for his campaign, far more than the 21-million-euro funding limit at the time.
“By 2011 Nicolas Sarkozy had already been accused by Moamer Kadhafi and his inner circle of having received financing for his campaign,” says Laske.
Sarkozy has consistently denied this. He is suing Mediapart, saying incriminating documents they published were falsified.
The website stands by its claims.
“A handwritten note by the former Libyan prime minister Choukri Ghanem speaks about payments made by Libya to Sarkozy’s team,” Laske explains.
“In 2016 several people, including Abdullah Sanussi, the ex-spy chief, and the intermediary Zied Takkiedine, told us they handed over the sum of five million euros to Sarkozy’s team.”
This is just one of dozens of questions that the former president will be expected to answer.
“Firstly Nicolas Sarkozy has never answered any questions on this case, not even to the press," Laske recalls. "We have compiled a list of 60 questions which remain unanswered.
“These questions are linked to his meetings with Moamer Kadhafi and in particular his requests for help with developing a civil nuclear programme, arms purchases and the pardon of Abullah Sanussi who was convicted of terrorism in Paris.”
This is not the only legal fight Sarkozy has on his hands.
Investigators have already said he should face trial for his failed 2012 reelection campaign - in the so-called Bygmalion affair.
And he is also being investigated for corruption and influence-peddling in a third case.