Former French President Nicolas Sarkozy is under formal investigation into an alleged spread of influence.
Nicolas Sarkozy, 59, appeared before a judge in Paris late Tuesday after a 15-hour questioning by anti-corruption police.
This is believed to be the first time a former French head of state has been held by police.
Nicolas Sarkozy’s lawyer Thierry Herzog and Magistrate Gilbert Azibert have also been formally investigated on the same charges.
A second magistrate summoned for questioning, Patrick Sasoust, had not appeared before a judge since Tuesday night.
When a suspect is formally investigated, 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 a test. Spreading influence can be punished by up to five years in prison and a fine of 500,000 euros ($ 684,000).
Nicolas Sarkozy was released from custody around midnight after appearing in court in Paris.
He was brought to court by the Judicial Police Service in Nanterre, west of the French capital, where he was questioned.
Paul-Albert Iveins, the lawyer representing Thierry Herzog, said the case was based only on “telephone taps … whose legal basis will be strongly disputed”.
“There is not much in this dossier, as none of the essential elements of what I have seen and what we could dispute support the allegations,” he added.
The investigation came as a result of a separate investigation into whether Nicolas Sarkozy received illegal funding for his 2007 election campaign from the late Libyan leader Muammar Gaddafi.
Nicolas Sarkozy hopes to challenge his candidacy for president again in 2017, and the investigation is seen as a blow to his hopes of returning to office.
Investigators are trying to find out whether Nicolas Sarkozy, who was president from 2007 to 2012, promised Gilbert Azibert a prestigious role in Monaco in exchange for information to investigate alleged illegal campaign funding.
They are examining allegations that Nicolas Sarkozy was warned that his phone was tapped as part of Gaddafi’s investigation.
Nicolas Sarkozy’s predecessor, Jacques Chirac, received a suspended sentence in 2011 for embezzlement and breach of trust while he was mayor of Paris, but he was never questioned in custody.
In February, an investigation was launched into whether Nicolas Sarkozy sought inside information to investigate the financing of his 2007 election campaign.
Nicolas Sarkozy was reportedly informed of the proceedings against him while it was decided whether his work diaries – seized as part of a funding investigation – should be kept in the hands of the justice system.
The Court of Cassation ruled in March 2014 not to return the diaries.
Investigators believe the former president was informed that his phone had been tapped as part of the investigation.
Nicolas Sarkozy insists the allegations against him are politically motivated. He is seeking to regain the leadership of the center-right UMP party later this year.