Former French president Nicolas Sarkozy has been handed preliminary charges over suspected illegal overspending on his failed 2012 re-election bid.
France capped presidential funding to 22.5 million euro (£17.5 million) in 2012.
Sarkozy, who lost out to Francois Holllande, is accused of spending 17 million euro (£13.2 million) over that.
The 61-year-old, who is now France's main opposition leader, has been questioned by prosecutors and could face fraud charges.
Preliminary charges mean magistrates have strong reason to believe a crime was committed.
But it gives them more time to investigate before deciding whether to send suspects to trial.
Several people close to Mr Sarkozy, including his former top adviser, also face preliminary charges in the case.
Sarkozy has already been fined 364,000 euro (£283,000) for overspending in the case.
Former French president Nicolas Sarkozy has described the terror attack at a gas factory as a "declaration war against France, democracy, and civilisation itself".
Sarkozy released a statement after the attack in which he called for the French public to be resilient.
This is a message, macabre and bloody in its implementation, from the perpetrator or perpetrators of this attack of a declaration war, not only against France and democracy, but to civilization, too.
We have the duty to defend ourselves with the utmost determination. This is the fight of all of France.
Never give in against the terrorist barbarity. Our thoughts go out to the families and friends of the victim and the injured.
Election projections for more than 2,000 councils across France show Nicolas Sarkozy's conservative UMP party taking the lead, blunting the rise of the far-right National Front.
The initial projections gave the UMP party 31% of the vote compared with 24.5% for the National Front and 19.7% for President Francois Hollande's ruling Socialists and their allies.
The Socialists were never expected to do well and had pinned their hopes on a high turnout to counteract the National Front.
Turnout was 51% for the first of two rounds of voting, compared with about 45% in the same elections in 2011.
Marine Le Pen's National Front party has made steady inroads as she tries to build a grassroots army of local officials to buttress her presidential ambitions.
Former French president Nicolas Sarkozy has announced his return to politics, saying he will seek the leadership of the opposition party UMP.
The French far-right leader Marine Le Pen has addressed a rally in Paris. She told her voters to make their own choice in the May 6th presidential election runoff. The two leading candidates - Nicolas Sarkozy and François Hollande - have been competing for the votes of her supporters.
As former French president Nicholas Sarcozy is released from detention by French authorities, he denies any wrongdoing and says the country's justice system has been 'politicised', reports Europe Editor James Mates
Former French President Nicolas Sarkozy has denied any wrongdoing and says he has not "betrayed" his country after being put under formal investigation for corruption.
Mr Sarkozy told Europe 1 radio the country's legal system was "being used for political means".
"The situation is sufficiently serious to tell the French people where we stand on the political exploitation of part of the legal system today," he said.
He added: "I say to all those who are listening or watching that I have never betrayed them and have never committed an act against the Republic's principles and the rule of law."
One of the allies of Nicolas Sarkozy has expressed doubts over the fairness and impartiality of one of the magistrates investigating the ex-French president over allegations of corruption.
"I question the impartiality of one of the judges," Christian Estrosi, the mayor of the southern city of Nice told France Info radio, accusing Hollande's government of having whipped up "an atmosphere of hate".
Former French President Nicholas Sarkozy has been placed under formal investigation by investigators after a hearing late on Tuesday night.
.As ITV News Europe Editor James Mates reports, this is one level below an official charge.
Fmr Pres #Sarkozy placed under formal investigation early today for influence peddling, corruption. 1 level below being officially charged.
Under French law, 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.
Former French President Nicolas Sarkozy has been escorted by police to a hearing before a judge in relation to allegations of corruption, influence-peddling and the "breach of professional secrets".
Mr Sarkozy has not been charged but he is now under "formal investigation", as are his lawyer and a judge suspected of being connected to the allegations.