|Sen. Serge Dassault|
The move comes a week after Dassault’s parliamentary immunity was lifted.
The 88-year-old is suspected of buying votes in Corbeil-Essonnes, east of Paris, where he was formerly mayor.
Dassault himself requested the lifting of his immunity in order to defend himself.
The veteran industrialist was taken into custody and interrogated by the police’s anti-corruption and fraud agency, a judicial source said.
He was questioned for the entire day before being released late Wednesday, with the questioning due to resume on Thursday.
Officials had said that, given his advanced age, Dassault could be moved to a Paris hospital if necessary during the 48 hours he can be held under French law.
Dassault is ranked by Forbes magazine as France’s fourth-richest man and the 69th-richest in the world, with an estimated fortune of 13 billion euros ($18 billion).
Investigators suspect Dassault of operating an extensive system of vote buying that influenced the outcome of three mayoral elections in Corbeil in 2008, 2009 and 2010, which were won either by Dassault or by his successor and close associate Jean-Pierre Bechter.
The result of the 2008 vote, won by Dassault, was invalidated by the Council of State after the body which oversees public administration discovered a series of payments which could have influenced the outcome of the election.
Its ruling did not require the same burden of proof as a criminal prosecution for vote buying would, but formal charges against Dassault seem likely.
Bechter has already been charged, as has Cristela de Oliveira, a former official in the mayor’s office who is suspected of allocating council flats to families in return for backing Dassault or Bechter.
Investigating judges are focusing on a huge sum of money transferred between France and Lebanon, including one totalling 18 million euros ($24 million), which they suspect could have been used to buy votes.
Dassault’s lawyers said last year that their client was regularly solicited for cash by people aware of his generosity but denied that payouts were made for electoral purposes.