Detectives hope post-mortems will shed light on a theory that a British family was shot dead by a hitman.
A picture has been released of Saad al Hilli - the father murdered near the village of Chevaline, near Lake Annecy, in the Haute-Savoie region.
French President Francois Hollande, speaking in London, where he is attending the Paralympic Games, said "everything will be done" to find the gunman who left four people dead and a young girl fighting for her life.
Three of them received bullet wounds to the centre of the forehead during the bloodshed.
Mr al Hilli and his wife Iqbal were named by neighbours as the victims. Their two children, who survived the attack, were named as eight-year-old Zehab and four-year-old Zaina.
Post-mortems are due to begin on the bodies later, and police hope they will give clues to why they were killed.
Iraqi-born Mr al Hilli, 50, a skilled computer engineer from Claygate, Surrey, was found slumped over the wheel of his bullet-riddled red BMW estate with the engine still running.
His dentist wife and her mother, who has a Swedish passport, were found shot dead in the back.
Public prosecutor Eric Maillaud said a passing cyclist, a British former RAF officer on holiday, discovered the bodies and alerted emergency services.
He also found Zehab, who collapsed in front of him near the car. She had been beaten around the head and shot in the shoulder. She is now fighting for her life in an induced coma at a hospital in the city of Grenoble.
Her sister Zaina was found alive hiding underneath the front passenger seat and legs of her mother - eight hours after the massacre. She has been admitted to another Grenoble hospital in "distress" and is receiving psychiatric care.
Both girls, who go to school in Claygate, are being guarded by armed police.
The body of a male cyclist - Sylvain Mollier, a father-of-three, from the nearby town of Ugines - was found near the BMW.
It is thought the factory worker inadvertently cycled into the scene of the attack, moments after overtaking the British cyclist. Mr Mollier, 45, was shot in the head, as was Mr al Hilli and his mother-in-law.
Mr Maillaud described the shooting as "horrific and alarming" and "a gross act of savagery", during a press conference in Annecy.
Mr al Hilli had been working as a freelance engineer for Guildford-based Surrey Satellite Technology after fleeing Saddam Hussein's Iraq, neighbours said.
He was known to security services and was put under Metropolitan Police Special Branch surveillance during the second Gulf war, the Daily Mail reported.
A Scotland Yard spokesman said they could not comment because he had not yet been formally identified.
Mr al Hilli had confided to neighbours about something that was troubling him in the run-up to his holiday.
He and his family had been staying in a caravan at a campsite popular with UK tourists called Le Solitaire du Lac, in Saint Jorioz, since Monday.
It is believed their neighbours at the campsite alerted police when they appeared to be missing.
No weapons were found at the scene of the shooting, which happened at around 3.40pm on Wednesday. Fifteen cartridges were found near the vehicle.
Only the windows had been shot through, leading police to speculate it may have been the work of a professional hitman. The BMW was removed from the scene late on Thursday for forensic tests to be carried out.
Stephane Bouchet, from local newspaper Le Dauphine Libere, told Sky News a witness two miles from the car park saw a car driving very fast away from the scene around the time of the shooting.
There are 60 police officers involved in the operation and the nearby area has been sealed off as investigations continue.
Surrey Police said it was assisting the French authorities and liaising with the Foreign and Commonwealth Office.