Three of the four victims of a shooting in the French Alps were shot in the head, a French prosecutor has said.
A man, named by UK neighbours as Saad al-Hilli, 50, from Surrey, and an elderly woman were found dead in a car near Lake Annecy. A French cyclist, found nearby, was also shot dead.
Mr al-Hilli's wife was also killed, and a daughter, four, hid in the car for eight hours before police found her.
Another daughter was found near the car with serious injuries.
Police said a British cyclist, who had served in the RAF, found the adults and child on a forest road.
Mr al-Hilli's wife was named by neighbours in Claygate as Iqbal, and the couple's daughters as Zainab, seven, and Zeena.
Annecy prosecutor Eric Maillaud said: "It was clearly an act of extreme savagery and it was obvious that who did this wanted to kill."
The motive for the attack remains a mystery, he added.
An automatic pistol was used, and the killer "targeted" the victims rather than indiscriminately firing into the car.
Zainab, found shot outside the British-registered car, has been transferred to a hospital in the city of Grenoble where she has been placed in a medically-induced coma. She is due to be operated on again.
She was shot once, and had head fractures. "She suffered a violent attack," Mr Maillaud said.
Both girls are under police protection in hospital.
Authorities have not confirmed Mr al-Hilli's name, saying only that they know who owns the car, and that the details matched the passport used to book a nearby campsite.
However, they could not match the driver's face with those details yet.
Mr Maillaud also said Iraqi passports had been recovered, and that the older woman had a Swedish passport. Formal identification of all the bodies was ongoing.
The family had arrived on 3 September at the campsite and had been due to leave by the end of the week.
Mr Maillaud said the British cyclist was passing along a road and saw a BMW with the engine still running.
He saw the older girl collapsing in front of him, and helped her into a recovery position, then called firefighters. Mr Maillaud said "without doubt he saved the girl's life".
He then discovered the other cyclist, who had overtaken him earlier, dead on the road. He broke the driver's window of the car, and saw three bodies inside.
The younger daughter was concealed beneath her mother and was not found until midnight.
But Mr Maillaud said that at the time the police were not looking for any more survivors.
She was found "terrorised, motionless, in the midst of the bodies" after fellow guests at the campsite told officers the family had two children, Mr Maillaud said.
The girl spent Wednesday night in hospital, with a nurse by her side all night. Police said they had spoken briefly to her.
French President Francois Hollande has said "everything will be done" by French authorities to find the killer, the AFP news agency reported.
Speaking at a press conference in London, where he is attending the Paralympic Games, the president said France stood "in solidarity" with Britain.
Prime Minister David Cameron expressed a similar desire to find out what happened, saying: "Obviously the faster we can get to the bottom of what happened, the better."
Police in Surrey have said they are assisting the French authorities and liaising with the Foreign and Commonwealth Office (FCO) following the shooting.
The British ambassador to France, Sir Peter Ricketts, said: "Clearly, this is a terrible, tragic event, a brutal murder, but also a traumatic experience for these two young girls."
Speaking in Annecy, he said consular staff had been with the youngest sister to give her support. "We are doing everything you would imagine we would do with a small girl who must be deeply, deeply traumatised, in a foreign country, not speaking the language."
He said staff were following up information about the family, but he said no relatives were expected from Britain at this stage. He also said he was satisfied that French authorities were doing a "fully professional job".
A neighbour of Mr al-Hilli, George Aicolina, said: "They were a very caring family and they always did things together. The father used to read to the girls quite regularly. It's an almighty shock.
"I was speechless [when I heard] and cried for a while. It's very sad to happen to such a young and lovely family.
"They were well established in the area, the two girls went to a local school. It's very difficult for me to talk about."
He said the young girls "played like kids do and it's very difficult to see how they will cope without a father and mother".
Many French web users have expressed incomprehension at the fact that the youngest girl was only discovered eight hours after police arrived.
"How can you know that the occupants of the car were dead if nobody opened the doors for eight hours?" wrote Maria on the website of the daily newspaper Le Monde.
It was not until 23:00 local time (21:00 GMT) that police found out from the family's neighbours at the campsite that the family had a second daughter, and launched a search involving a helicopter and police dogs, one report said.
Police had believed only one child was involved with the scene because only one child seat was found in the car.
The investigators said there were several reasons why the youngest girl was not found earlier, including that police were told not to disturb the scene before the arrival of forensic investigators; and they did not want to compromise the ballistics investigation by opening the car doors because some of the windows had cracks made by the bullets.
Earlier reports said a helicopter with thermal imaging was also used, but did not detect the girl, who may have been concealed under the bodies.
Officials at the scene also tried to look through the car windows, but could not detect any movement.
The dead French cyclist was identified as Sylvain Mollier. His wife contacted police after he failed to return from his ride.