Correction: An earlier version of this article incorrectly said that a French magistrate opened a formal investigation against former president Nicolas Sarkozy in a campaign funding case. The investigation has been underway for some time, but the judge’s action Thursday made Sarkozy a suspect in the case. This version has been corrected.

The accusation, brought by an investigating magistrate in Bordeaux, was seen as a suggestion that Sarkozy sought to obtain illegal funds to finance his successful presidential run from Lilianne Bettencourt, who is ranked as France’s richest woman. (ERIC FEFERBERG)

A judge filed preliminary charges against former French president Nicolas Sarkozy on Thursday, accusing him of abusing the confidence of an heiress during fundraising for his 2007 election campaign.

The action by an investigating magistrate in Bordeaux was seen as a suggestion that Sarkozy sought to obtain illegal funds to finance his successful presidential run from Lilianne Bettencourt, who is ranked as France’s richest woman.

After a single five-year term, the conservative Sarkozy was defeated in May by President Francois Hollande of the Socialist Party. Although ostensibly retired from politics, Sarkozy has remained in the spotlight and, according to press accounts, has told friends that he might be forced to run again in 2017 to save France from economic disaster.

Bettencourt, 90, inherited the L’Oreal cosmetics empire and has been a longtime donor to political and charitable causes in France. But in recent years, she has been in court with family members several times over their concerns that she is no longer able to manage her fortune and is being taken advantage of by friends and employees.

The preliminary charges, announced by Sarkozy’s attorney, Thierry Herzog, were the climax of a day-long interrogation of the former president and several members of Bettencourt’s household staff. Herzog denounced the charges as “incoherent on the legal level and unjust” and said he would begin work immediately on an appeal to a Bordeaux court.

Thursday’s legal step, called “mise en examen,” followed months of investigation during which Sarkozy had been questioned at length but was considered to be a witness. It amounted to a formal notification to Sarkozy that he is no longer just a witness but suspected of a crime in an investigation that may lead to a trial if the prosecutor considers the investigating magistrate’s case strong enough.

Sarkozy has steadfastly denied that he received any money from Bettencourt or her late husband, Andre. He said he visited their home only once during the 2007 campaign to see the ailing Andre Bettencourt, himself a former political figure who died in November that year.

Sarkozy left the office of Investigating Magistrate Jean-Michel Gentil late Thursday evening without commenting. But his followers in Paris from the conservative Union for a Popular Movement (UMP) party were quick to voice their outrage on television panels. “This does not seem serious,” said Thierry Mariani, a UMP activist.Valerie Debord, another UMP stalwart, said that “a certain number of people” were out to get Sarkozy, suggesting the judge’s decision was politically motivated.

Gentil inherited the investigation into Sarkozy’s fundraising after it was moved to Bordeaux from Paris to escape relentless publicity surrounding the charges in the capital.

The probe into Sarkozy’s fundraising coincided with related charges from Bettencourt’s daughter that a society photographer had abused the elderly widow’s confidence over several year to obtain money and valuable gifts. It included testimony from a major-domo who tape-recorded meetings at Bettencourt’s home and from an accountant who said she was asked to withdraw cash from a bank account that was to be handed over to Sarkozy’s main fundraiser by Bettencourt’s wealth manager.