Paris: Former French President Nicolas Sarkozy came out fighting on Friday after he was placed under investigation for exploiting the mental frailty of the country’s richest woman to raise election funds, with his lawyer rejecting the case as flawed.

A Bordeaux magistrate launched an inquiry on Thursday into whether Sarkozy took advantage of 90-year-old L’Oreal heiress Liliane Bettencourt, after she was declared in a state of dementia, to help raise money for his 2007 election campaign.

The “abuse of weakness” case threatens to scupper any political comeback for Sarkozy, who was unseated by Socialist Francois Hollande last year, by leaving him under a cloud of suspicion for months or even years.

The 58-year-old, who says he is innocent, hinted this month he could use his continued popularity among conservative voters to run again for president in 2017.

His lawyer Thierry Herzog said on Friday he would seek to annul the formal investigation, which is the final step before a suspect is accused of a crime and could take years to complete.

“Mr Sarkozy will carry on fighting this but at the same time he believes the treatment that has been meted out to him has been disgraceful,” Herzog told RTL radio.

“Do you really think the case both for the prosecution and for the defence is being studied here?” he said, pointing to repeated interviews conducted by investigating magistrate Jean-Michel Gentil of members of Bettencourt’s household staff in an effort to get incriminating evidence.

Allies of Sarkozy also leapt to his defence, with one suggesting the timing of investigation was politically motivated to distract attention from a scandal surrounding one of President Hollande’s ministers.

While a formal investigation could take years, a successful appeal could quickly halt the inquiry.

Bettencourt was declared in a state of dementia in 2006 and was placed under the guardianship of her family in 2011.

The public prosecutor said on Thursday that Sarkozy was being investigated “for taking advantage of a vulnerable person in February 2007 and during 2007 to the detriment of Liliane Bettencourt”, a crime punishable by up to three years in jail.

Initial suspicions over funding were fuelled three years ago when a woman who worked as an accountant for Bettencourt alleged that a large cash withdrawal was earmarked for Sarkozy’s presidential election campaign.

The investigation came two days after Hollande’s Budget Minister Jerome Cahuzac stepped down to fight accusations of tax fraud after police said a leaked recording of a male voice admitting to holding a secret Swiss bank account was probably his. Cahuzac denies any wrongdoing.