Former French president Nicolas Sarkozy has been placed under formal investigation over alleged influence peddling.
The 59-year-old, who was leader from 2007-2012, appeared before a judge in Paris late on Tuesday after 15 hours of questioning by anti-corruption police.
It is thought to be the first time a former French head of state has been held in police custody, the BBC reports.
Mr Sarkozy's lawyer, Thierry Herzoog, and senior prosecutor Gilbert Azibert were also placed under formal investigation over the allegations.
When a suspect is placed under formal investigation, he or she is then examined by a judge, who determines whether there is sufficient evidence for the suspect to be charged.
The step often, but not always, leads to trial. Influence-peddling can be punished by up to 10 years in prison and a fine of €150,000.
After allies of Mr Sarkozy accused the justice system of political bias, Socialist Prime Minister Manuel Valls said on Wednesday the allegations against Mr Sarkozy were serious and the investigation was being carried out independently of the government.
Paul-Albert Iweins, the lawyer representing Mr Herzog, said the case rested only on "phone taps ... whose legal basis will be strongly contested. There's not a lot in this dossier, since none of the material elements of what I've seen, and what we could contest, support the accusations."
The inquiry arose out of a separate investigation into whether Mr Sarkozy had received illegal funding for his election campaign in 2007 from the late Libyan leader, Muammar Gaddafi.
Mr Sarkozy is hoping to challenge again for the presidency in 2017 and the inquiry is seen as a blow to his hopes of returning to office.
Investigators are trying to find out whether Mr Sarkozy had promised a prestigious role in Monaco to Mr Azibert, in exchange for information about an investigation into alleged illegal campaign funding.
They are looking into claims that Mr Sarkozy was warned his phone was being bugged as part of the Gaddafi inquiry.