Ex-French President Nicolas Sarkozy has been placed under formal investigation over alleged influence peddling.
He appeared before a judge in Paris late on Tuesday after 15 hours of questioning by anti-corruption police.This is thought to be the first time a former French head of state has been held in police custody.
Mr Sarkozy's lawyer, Thierry Herzog, and senior prosecutor Gilbert Azibert were also placed under formal investigation over the allegations.
A second prosecutor called in for questioning, Patrick Sassoust, had not appeared before a judge as of Tuesday night.
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 euros (£120,000; $205,000).
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.
Writing in the centre-left daily Liberation, Eric Decouty argues that Mr Sarkozy must take responsibility for his actions if he wishes to return to politics. "Even if the former head of state has never made morality his chief virtue, he cannot scorn certain values essential to our democracy," he says.
The French justice system may now be doing the "dirty work" of Mr Sarkozy's own party, Patrice Chabanet suggests in an editorial for regional daily Le Journal de la Haute-Marne. Other figures in the party like former prime ministers Francois Fillon and Alain Juppe "want to turn the page of Sarkozyism", he argues. Even if Mr Sarkozy emerges from his legal troubles exonerated of blame, the cost to his political career may be too great, he suggests.
He had been brought to the court from the judicial police office in Nanterre, west of the French capital, where he had been interrogated.
Lawyer Thierry Herzog (l) and magistrate Gilbert Azibert (r) are being investigated along with Mr Sarkozy (c)
"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," he added.
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, 59, who was president from 2007 to 2012, 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.
Mr Sarkozy's predecessor, Jacques Chirac, was given a suspended prison sentence in 2011 for embezzlement and breach of trust while he was mayor of Paris but he was never questioned in custody.
October 2013: A criminal investigation into allegations he solicited secret campaign financing in 2007 from France's richest woman, Liliane Bettencourt, is dropped
April 2013: Judges open an inquiry into allegations that the Gaddafi regime helped finance his 2007 election campaign
February 2014: Named as a witness in investigation into funding for Edouard Balladur's unsuccessful presidential bid in 1995
A number of other inquiries are under way into wrongdoing by senior officials during his presidency, in which he has not figured directly
It is alleged that Mr Sarkozy was kept informed of proceedings against him while a decision was made over whether his work diaries - seized as part of the funding inquiry - should be kept in the hands of the justice system.
The Court of Cassation, where Mr Azibert holds the post of first advocate general, ruled in March 2014 that the diaries should not be returned.
Investigators believe the former president was tipped off that his phone was being bugged as part of the inquiry.
Mr Sarkozy insists the allegations against him are politically motivated.
But the BBC's Hugh Schofield in Paris says it is clear they represent another obstacle in the way of his planned return to frontline French politics.
The former president is seeking to regain the leadership of the centre-right UMP party later this year.
Mr Sarkozy is a step closer to coming to trial. The judges investigating this have decided that there is a case to answer although a trial is not inevitable. It does mean that there is a much bigger, darker cloud of suspicion hanging over him.
Worried by the prying of investigators into claims of illegal party fund-raising, it is alleged that Mr Sarkozy used a judge as point-man in the High Court of Appeal to tell him how proceedings against him were progressing. More serious is whether this judge tried to influence decisions in Mr Sarkozy's favour.
The former president was expected to announce his political comeback later this year, and his supporters are extremely suspicious about the timing of this latest development. It will be much harder now to launch a bid for leadership of the opposition centre-right, with the prospect of criminal proceedings hanging over him.
Sarkozy detention raises 'plot' suspicions
