The complaint came from a lawyer acting for victims of a 2002 bombing in Karachi that investigators believe may be linked to a long-running corruption and illegal party-financing case.
France’s constitution shields presidents from testifying, being investigated and prosecution until a month after their term is up, which for Sarkozy was on Friday.
His immunity had kept him from being involved in probes into a submarine sale to Pakistan in the 1990s and, separately, into relations between him, his party and France’s wealthiest woman.
In the so-called “Karachi Affair”, judges are trying to unravel dealings by middlemen and possible kickbacks linked to France’s sale of Agosta class submarines to Pakistan.
Investigators are looking into whether the sale was the source of illegal party financing during the 1995 presidential campaign. They are also investigating whether a 2002 bomb blast in Karachi that killed 11 French nationals was a reprisal for Paris’ decision to stop paying commissions on the sale.
A lawyer for the victims filed the complaint, accusing Sarkozy and his aides of illegally gaining access to elements of the inquiry, compromising investigators’ independence.
The lawyer, Olivier Morice, said an official denial by Sarkozy’s office last September that he had any involvement in the case revealed that he was illegally privy to elements of the investigation even though he was not part of the probe.
The presidential palace denied at the time that it had access to documents in the case, which was widely reported on by media and which cast a legal cloud over Sarkozy’s unsuccessful bid for a second term.
Sarkozy risks being entangled in a second, unrelated case in which investigators are looking into whether cash withdrawals from the account of L’Oreal heiress Liliane Bettencourt were used to finance Sarkzoy’s 2007 campaign.
Sarkozy’s lawyer has handed over his 2007 diary to investigators to fight allegations that he visited Bettencourt during the campaign, Le Journal du Dimanche reported.
Legal sources told the weekly publication that investigators were considering searching Sarkozy’s house.
Socialist Francois Hollande defeated Sarkozy last month, promising to boost growth, cut unemployment and rid state business of murky affairs which have dogged it in the past under both right and left-wing administrations.
Hollande has vowed to change the rules so that a president, starting with himself, can be questioned while in office on judicial matters that pre-date the presidential mandate.
Sarkozy’s predecessor, Jacques Chirac, who ruled France from 1995 to 2007, was handed a two-year suspended jail sentence in December after a court found him guilty of misusing public funds for political purposes when he was mayor of Paris.