French ex-President Nicolas Sarkozy has arrived at a court in Bordeaux to be questioned over allegations he received illegal campaign donations in 2007.
Mr Sarkozy is suspected of accepting thousands of euros from L’Oreal heiress Liliane Bettencourt, the country’s richest woman.
Police raided his home and offices in July as part of an inquiry ordered by investigating judge Jean-Michel Gentil.
Mr Sarkozy, who lost presidential immunity in May, denies all wrongdoing.
Although he has stepped back from frontline politics since his defeat by Socialist challenger Francois Hollande, Mr Sarkozy is rumoured still to harbour ambitions of running for re-election in 2017, the BBC’s Christian Fraser in Paris reports.
The outcome of the investigation could determine whether the former president will make his widely anticipated return, our correspondent says.
Cash envelopes
Judge Gentil is leading the investigation into allegations that staff acting for Mrs Bettencourt gave 150,000 euros (£120,600) in cash to Mr Sarkozy’s aides during his successful 2007 campaign to become president.
Individual campaign contributions in France are limited to 4,600 euros.
Mrs Bettencourt’s former accountant, Claire Thibout, alleges Mr Sarkozy’s campaign treasurer at the time – Eric Woerth, who later became budget minister – collected the cash in person.
She also revealed in a leaked police interview that Mr Sarkozy, while mayor of Neuilly from 1983 to 2002, paid “regular” visits to the Bettencourt house, our correspondent says.
The former president has dismissed as mere gossip claims that he took envelopes stuffed with cash.
Mr Woerth, who was forced to resign as UMP party treasurer in July as a result of the scandal, is already under formal investigation over the 150,000 euro payment allegations.
The allegations surrounding Mr Sarkozy and Mr Woerth first surfaced in connection with a trial over the estimated 17bn euro fortune of Mrs Bettencourt, 87, whose father founded the L’Oreal cosmetics giant.
Both Mr Woerth and Mr Sarkozy deny any wrongdoing, as does Mrs Bettencourt.