Former French President Nicolas Sarkozy has been placed under formal investigation over alleged influence peddling.
He appeared before a judge late on Tuesday, after presenting himself early that morning for police questioning, which lasted 15 hours.
This is thought to be the first time a former French head of state has been held in police custody.
Sarkozy's lawyer, Thierry Herzog, was also placed under formal investigation as part of the same case.
A magistrate, Gilbert Azibert, also appeared before a judge.
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.
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The inquiry began when judges examined allegations that Sarkozy received illegal funding for his re-election campaign from the former Libyan leader, Muammar Gaddafi.
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 Sarkozy, 59, who was president from 2007 to 2012, had promised a prestigious role in Monaco to Azibert, in exchange for information about an investigation into alleged illegal campaign funding.
Ex-French president Nicolas Sarkozy detained for questioning http://t.co/Fnl2OJDOAU
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They are looking into claims that Sarkozy was warned his phone was being bugged as part of the funding probe.
Azibert, one of the most senior judges at the court of appeal, was called in for questioning on Monday as was another judge, Patrick Sassoust.
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.