A four-year-old girl and her older sister were under "extremely high" protection as police hunted for the attacker who gunned down her mother, father and grandmother at a French beauty spot.
The little girl was discovered hidden beneath the legs of her dead mother in a British-registered BMW near Chevaline in the French Alps, where they had been camping.
Her father, found slumped in the front of the car, was named as Saad Al-Hilli, 50, from Claygate, Surrey. He was born in Baghdad, Iraq.
Mr Al Hilli is understood to have been the secretary of a Wiltshire-based aerial photography company, AMS 1087, since 2007.
The mother was also believed to be 50 years old while the grandmother was aged 77. The children were said to be seven and four.
Police had missed the four-year-old girl when they found the car and could not open the bullet-riddled doors over fears ballistic evidence would be destroyed, officers said.
A senior police source said the terrified child had only been found at midnight when witnesses at Le Solitaire du Lac campsite told detectives the family had two children, not one. Only then did they "break with protocol" and open the doors to find the girl.
He said she was very small and young for her age, and had not appeared to have understood what had happened to her family.
Along with her seven-year-old sister, who was in hospital after being beaten and left for dead, he said they were "key witnesses" who were being heavily guarded.
The source also dismissed suggestions the attack may be linked to two attempted car-jackings, describing the massacre as a "very particular modus operandi" in a spot popular with tourists.
The family was believed to have been coming to the end of their holiday, having arrived in France at the end of August.
Eric Maillaud, the Annecy prosecutor, said that when forensic officers began a detailed examination they found the girl who had remained hiding, silently, in terror, for up to eight hours.
"When the investigators got into the car they discovered a little girl, who was frozen still and uninjured," he said.
"She could not tell the difference between the good guys and bad guys. She spontaneously began to smile and speak in English when the policeman took her in his arms and pulled her out of the car."
He added: "The little girl spoke English. She had heard the noises, the cries but she couldn't say more, she is only four years old."
An eight-year-old girl was discovered lying on the road in a critical condition near the BMW people carrier, while a French male cyclist, who had also suffered gunshot wounds, was also found dead close by.
He was named by French media as Sylvain Mollier, a father-of-three in his 40s from Ugine en Savoie. He reportedly worked for Cezus, a metal manufacturing firm.
The older girl had been airlifted to hospital and was said to be in a stable condition at Grenoble University Hospital.
A French newspaper reported she had not been shot but was brutally beaten before being left for dead with a fractured skull, nine miles from where the family had been camping at Le Solitaire du Lac campsite in Saint Jorioz.
Police are unsure when they will be able to question the girl, who was in a state of shock.
Kara Owen, the deputy British ambassador, is in Grenoble at the injured girl's bedside in hospital before going to the scene of the massacre at Chevaline.
Officers said the younger girl had remained undiscovered for eight hours "due to procedure".
The source explained: "The crime scene was kept frozen until forensics experts arrived from Paris during the night.
"This meant that the dead bodies had to remain in the place where they fell. The little girl was well hidden under her mother’s legs, and clearly was in a state of shock."
The identity of the victims "remains to be verified", Mr Maillaud said.
The site reported a family including parents and a grandmother missing.
One woman, who was staying at the same campsite, said: "I saw the two women yesterday with the two little girls collecting apples. Everything seemed normal, but I didn't know them.
"It was the first year that they had been seen here. It is terrible. The atmosphere is heavy, nobody is speaking."
French media reported the father, thought to be in his 50s, was in the front of the BMW while the two women were in the back of the car.
"The three bodies found in the car could be the father, mother and grandmother," said Benoit Vinnemann, Lieutenant Colonel in the Chambery gendarmes . "In any case, that is the make-up of the British family described by the campsite who reported them missing on Wednesday night."
Lt. Col Vinnemann said: "The main witness, a cyclist who discovered the grisly scene, said he was overtaken by another cyclist on the climb that leads to the parking lot where the shooting took place.
"Arriving there, he found the cyclist on the ground with gunshot wounds near a car. In the vehicle, a man and two women, has also been shot. On the other side of the car, a child of 6-8 years old was alive. He placed her in the recovery position until help arrived. She had been very badly beaten."
Mr Maillaud confirmed the victims were British and said the main theory was that the attack was a crime gone wrong but said "a family drama cannot be excluded".
"The owner, the driver of the vehicle, is established as a British citizen. For the others, presumably his family, it remains to be seen," the prosecutor said.
"He had left his passport details at the Saint-Jorioz campsite."
Later, it emerged there had been two attempted car-jackings by an armed gang 50 miles away on the same night. Police were investigating links between the attempted thefts and the shooting.
A police source told France's Europe 1 radio: "Current theories are either that the family were the victims of an armed robbery or that they disturbed a drug deal taking place."
Detectives found 15 spent bullet casings from an automatic gun at the scene of the killing.
The shooting happened in a tree-lined car park near the picturesque village of Chevaline, a popular destination for holiday-makers and tourists.
The Foreign Office said that the British Embassy's deputy head of mission in France was at the scene of the shooting.
"She is liaising with the local authorities and police to get more information," a spokesman said.
Didier Berthollet, the mayor of Chevaline, told a local newspaper that “the victims were not from the village”.
He added: “We have never seen such horror on our doorsteps before. The police have interviewed everyone in the village hoping to find a witness. There are only 70 homes, so it didn’t take them long.”
Earlier this summer the Foreign Office warned British tourists driving on the Continent that they were regarded as “easy targets” by gangs which staged accidents to make them stop before robbing them. A French police officer said: “It’s the time of year, the thieves go for tourists who they see as rich.”
France recently tightened its laws on illegal firearms amid a worrying rise in the use of guns by criminals. In July a gunman using an assault rifle shot dead two people and injured five at a nightclub in Lille after being turned away.
In March, Mohammed Merah, who claimed to be linked to al-Qaeda, killed four people at a Jewish school and three soldiers in southern France. He was killed after a 32-hour siege in Toulouse.
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