A four-year-girl who was in a car when her parents and grandmother were shot dead stayed hidden under her murdered mother's skirt for eight hours after police arrived.
Firemen and police officers, under orders to leave the British-registered BMW untouched pending the arrival of forensic experts, failed to spot her.
Yesterday French investigators said they still did not know why the family of British holidaymakers were slain at a remote forest car park near the French Alpine village of Chevaline.
Four people were found dead on the road: a man in the driver's seat; his wife and mother-in-law in the back seat; and a French male cyclist who appeared to have nothing to do with the family.
An older daughter was shot in the shoulder and suffered multiple and "extremely violent" blows to the head during Wednesday's attack.
Three of the four killed were shot in the head in what the prosecutor in charge of the case called an act of "extreme savagery". Eric Maillaud said he could not say whether the unexplained attack had the hallmarks of a professional assassination.
But he added: "It was clearly an act of extreme savagery and it was obvious that whoever did this wanted to kill."
Maillaud said the elder sister had been placed in an induced coma ahead of further surgery in a hospital in Grenoble.
Maillaud said the victims were discovered by a veteran of Britain's Royal Air Force who had a second home in the area and had cycled into the car park at 3.48pm.
The cyclist who was killed had overtaken the veteran minutes earlier. As the Briton arrived in the car park, the elder girl stumbled towards him before collapsing to the ground.
He immediately alerted emergency services in an action that probably saved her life, according to the prosecutor.
Several witnesses reported seeing a car speeding away from the scene around the time of the attack.
Local police defended the decisions that led to the four-year-old being left in the car for so long. Rescuers had eyed the crime scene but were told to wait for special investigators to arrive.
"Firemen, technicians and doctors all looked into the car through the holes in the windows but none of them saw the girl," a spokesman said.
A helicopter equipped with a thermal camera took images of the car to check if there were any other bodies inside but also failed to detect the girl. "She was so close to her mother, they appeared as one mass," he said.
The girl was only found after midnight, but was doing fine physically, Maillaud said.
She described hearing cries and asked investigators where her family was. She was taken into police care.
The dead man was Saad al-Hilli, 50, who was born in Baghdad and lived with his family in Surrey. His mother-in-law had a Swedish passport.
Hilli's accountant, Julian Stedman, said he was a director of an aerospace firm, Sctech Limited. Stedman said Hilli was a computer design specialist.
"He would be working for several months for one company and then possibly move on when the work dried up," he said.
"I never dreamed it would be him. It's a total and utter shock to me."
He said the family had taken a caravan with them on holiday to the French Alps.
A friend of the family delivered white flowers that were taken by a uniformed policeman outside the house. Hilli was a "nice guy", said the friend, who refused to be identified.
Additional reporting by Associated Press