Paris, France (CNN) -- French police were questioning four men Thursday as part of the widening investigation into the finances of France's richest woman, L'Oreal heiress Liliane Bettencourt.
The four include Patrice de Maistre, Bettencourt's financial adviser, and Francois-Marie Banier, a photographer friend of Bettencourt's at the center of an ongoing trial.
The prosecutor's office in the Paris suburb of Nanterre, where that trial is being held, confirmed that police were questioning de Maistre and Banier along with Fabrice Goguel, Bettencourt's former tax lawyer, and Carlos Vejarano, who manages an island in the Seychelles that Bettencourt reportedly gave to Banier.
Police have been investigating allegations that Bettencourt, 87, illegally funded French President Nicolas Sarkozy's election campaign.
The allegations came from Bettencourt's former bookkeeper, who told a French investigative website last month about envelopes of cash that were given secretly to Sarkozy and Labor Minister Eric Woerth, who used to be France's budget minister.
The police investigation came on the sidelines of a trial already under way in Nanterre involving Bettencourt and Banier.
The heiress' daughter, Francoise Bettencourt-Meyers, accuses the photographer of bilking her mother out of a billion euros that she allegedly gave to him. She claims her mother is not mentally competent to handle her own affairs, and she took the case to court to recover the money.
The trial is on hold while police investigate the campaign financing allegations.
Both women are on L'Oreal's board of directors.
Wednesday, Bettencourt-Meyers launched a separate civil lawsuit that seeks to have her mother declared legally irresponsible and placed under the authority of the court.
It is the daughter's second attempt to declare her mother incompetent, after a judge refused Bettencourt-Meyers' initial case last year because of a lack of medical expertise.
Bettencourt fought back against the lawsuit Wednesday, telling France 3 Bretagne about her daughter, "She should look after herself and I'll take care of me."
Bettencourt added, "I'm hurt and vexed at the same time, because I tell myself how, after so many years, someone who has lived so close to me has such petty reactions."
The heiress later said she had asked de Maistre, "whom I have complete confidence in," to organize an independent audit of the three companies that manage her fortune.
CNN's Saskya Vandoorne contributed to this report.