Police baffled by shooting of Hélène Pastor, wealthy landowner in the tax haven, whose chauffeur was also killed in the attack

A wealthy Monaco heiress shot two weeks ago in a mysterious attack on the French Riviera has died of her injuries in hospital.

Hélène Pastor, 77, said to be close to Monaco's royal family, and nicknamed the "vice princess", had been visiting her son in hospital when an unknown gunman opened fire on her Lancia Voyager car.

Her chauffeur, who was seriously injured in the attack that has baffled detectives, died four days later. Pastor was taken to hospital with injuries to her face, neck, chest and abdomen, but died on Wednesday.

She had spent two hours before the attack at the bedside of her son Gildo, who had suffered a stroke, and left the Archet hospital in the west of Nice in the early evening. As her car pulled out of the hospital on to the main road, a man leaped out from behind a parapet wielding a sawn-off shotgun and fired into the passenger side.

After shooting a first time, the killer leaned into the slowly moving car and shot a second time, critically injuring driver Mohamed Darwich, 64, who had worked for Pastor for 15 years. CCTV images show the shooter running off with a second man. The car continued a further 20 metres before crashing into a parked vehicle.

"Unfortunately, the images are not perfect and until now we haven't been able to identify the murderers, who were disguised," said a police spokesperson.

A report in the French daily Le Figaro said investigators suspected the two were members of Italy's most notorious organised crime gangs – either 'Ndrangheta or the Camorra. Both clans are said to have gained a strong foothold in the French Riviera's property sector, in which the Pastor family are key players.

Pastor, the sister of Michel Pastor, the former chairman of Monaco football club who died in February, was described by shocked friends as a "model of wisdom and discretion".

The Pastor family has a huge portfolio of property and land in Monaco estimated at 50,000 sq metres – part of a building dynasty established by Hélène Pastor's grandfather, Jean-Baptiste, an Italian immigrant stonemason from a poor family in Liguria, who arrived in Monaco in the 19th century. After building Monacos first football stadium, the firm was taken over by his son Gildo who bought up swaths of seafront real estate at bargain prices after the second world war. When he died in 1990 his three children, Hélène and her late brothers, Michel and Victor, inherited his fortune.

The three branches of the Pastor family are believed to own between 3,000-4,000 flats of a total of 20,000 in the 0.8 square mile (2 sq km) principality, which is worth an estimated €20bn (£16bn) .They are also friends of the Monaco royal family. The heiress controlled five mansion blocks on Avenue Princesse-Grace and Avenue de Grande-Bretagne – prestigious addresses rented at about €15,000 a month for a four-room flat.

After the attack, Prince Albert said he was "deeply upset" and offered the Pastor family his "very deep support".

Police, who first described the attack on Pastor's car as an "ambush" and an "attempted execution", admitted they had no idea whether it was Pastor or her chauffeur who was the target of the gunmen, and said the choice of weapons did not suggest a professional assassin or the mafia.

"All lines of inquiry remain open," a police source working on the murders told Le Nouvel Observateur magazine. "The inspectors of the Nice criminal division are examining the weapon, which is not a favourite of the big professional bandits."

Police say they are now looking into any family secrets that may have provided a motive for Hélène Pastor's murder.