Saad al Hilli, 50, who was originally from Iraq, was shot in the head alongside his dentist wife, Iqbal, and a woman believed to be her mother.
Mr al Hilli was known to UK security services and was under surveillance during the second Gulf war, according to reports.
A passing 45-year-old French cyclist, Sylvain Mollier, was also shot dead.
Three of the four who were killed were shot in the middle of the head, but the man investigating the spree played down suggestions of “professionalism” in the attack.
Police said the motive for the attack remained a mystery but said there were signs of a vehicle braking at the scene.
Investigators said no weapon had been found and no arrests made.
It was also unclear if the shootings were carried out by one killer or several.
One theory is that shots could have been fired during a bungled armed robbery, with the cyclist being a witness to the crime.
There was widespread shock yesterday when the Hillis’ four-year-old daughter, Zeena, was found alive in the BMW estate underneath the bodies of her relatives eight hours after the massacre.
The Hillis’ seven-year-old daughter, believed to be called Zainab, was in a medically-induced coma in Grenoble University Hospital after being repeatedly beaten around the head and shot in the shoulder in the attack.
Public prosecutor Eric Maillaud said yesterday: “I won’t say it was professional, what I will say is it was tremendous savagery. And what is certain is that somebody wanted to kill.”
But one of the family’s neighbours in the upmarket village of Claygate in Surrey said he was going to alert police to something Mr al Hilli said to him before travelling to the Le Solitaire du Lac campsite in Saint-Jorioz, close to the Swiss border.
Jack Saltman told the Richard Bacon show on Radio 5 Live: “I know one little thing which I am not prepared to speak [about] at the moment.
“I will tell the police about it. It was something Saad said to me before he went, but at this stage I do not feel I can disclose that, but I will tell the police exactly what he told me before he left.”
The powerful BMW, which was moved by police yesterday, was found surrounded by spent bullet cartridges in a car park near footpaths on the outskirts of a forest near Lake Annecy, a picturesque region popular with tourists.
Mr Maillaud described the scene as being like something from a film and said 15 cartridges were found around the car and a “very large number” of shots had been fired.
The firearm used is believed to have been an automatic pistol.
The two dead women were found in the back seat of the car with a number of bags.
A British cyclist, a former RAF serviceman who had been overtaken by the French rider, discovered the grisly scene in a quiet car park, Mr Maillaud said.
Zainab came towards him badly injured and collapsed, and he gave her first aid before finding Mr Mollier beside the still-running car.
Breaking a window to turn off the engine, he discovered the three bodies inside.
He then called emergency services.
The four-year-old lay undiscovered as police waited for forensic experts to arrive at the scene from Paris.
She was found “terrorised, motionless, in the midst of the bodies” after fellow campers at a nearby site told officers the family had two children, Mr Maillaud said.
He defended the delay in finding her as he revealed she was receiving psychiatric treatment.
French President Francois Hollande said authorities will do their ‘utmost to find the perpetrators’ who killed three people and left a young girl fighting for life in the French Alps.