Jacqueline Veyrac, 76, the millionaire owner of the Michelin-starred La Reserve restaurant in the French Riviera city of Nice was snatched last Monday as she was getting into her SUV and bundled into a waiting van.
Veyrac, who also owns the five-star Grand Hotel in nearby Cannes, was released two days later after being spotted by a passerby bound and gagged and lashed to the van's floor.
Nice prosecutor Jean-Michel Pretre said that Veyrac's abductors bound her wrists and ankles and sealed her eyes and mouth with tape. She sustained several injuries in her efforts to break free, he added.
The passerby first noticed that a number plate on the vehicle was a bit loose, revealing another one underneath, before spotting Veyrac inside.
Authorities have charged three other people for their part in the conspiracy, and all six have been remanded in custody.
They all face life imprisonment if convicted.
Separately, a former police officer who now works as a private detective was charged over failing to alert authorities to the group's plans and subsequently bailed.
Investigators believe the restaurateur, identified only as Giuseppe S, harboured a grudge against Veyrac.
Originally from Turin, he managed La Reserve from 2007 until 2009 when his company went into liquidation, causing him to resent Veyrac.
The kidnapping was a bid to recover money lost during the liquidation by demanding a ransom from those close to Veyrac, investigators said.
The former press photographer, Luc G — also known as “Tintin” — is accused of fitting a tracking device to Veyrac's car.
And a British citizen, who served in the UK's special forces and is now homeless in Nice, is accused of providing surveillance for the gang.
The other three people charged with involvement in the case are thought to be gang members who took part directly in the kidnapping of Veyrac, who was abducted by three men in the heart of Nice.
Veyrac, whose husband died five years ago, co-owns the Grand Hotel, as well as La Reserve, with one of her sons.
The Grand Hotel is one of the establishments on the palm-lined Croisette boulevard that roll out the red carpet each May for movie stars attending the Cannes Film Festival.
Veyrac was targeted in another attempted kidnapping three years ago but the motive was never clear.
Investigators are seeking to determine whether the two events are linked.