Police were probing Friday whether a family feud could be behind a shooting that killed three members of a British-Iraqi family in the French Alps after questioning of a child survivor failed to provide new clues.

Local prosecutor Eric Maillaud said British police had told French authorities of a financial dispute between the British man killed in the shooting and his brother, but he cautioned against drawing early conclusions.

"It seems that there was a dispute between the two brothers about money. This seems to be credible information coming from the British police," Maillaud told AFP.

"The brother will have to be questioned at length. Every lead will be meticulously followed."

He added however that it was difficult to imagine how a family feud could "pass from a financial dispute to a quadruple murder".

A French police source said the brother of victim Saad al-Hilli, a 50-year-old Briton born in Iraq, had presented himself to British police on Thursday to proclaim his innocence and cooperate in the probe.

Maillaud also said police had questioned the four-year-old girl who spent eight hours hiding in a car beneath her dead mother's skirts after the shooting but that she was unable to provide significant information.

"She was questioned again last night, but without giving many more details. We have to be extremely careful about the declarations of a traumatised little girl," he said.

Maillaud said autopsy results on the victims' bodies were due on Friday afternoon and that the response to a formal request for DNA samples from Britain was expected to arrive on Saturday.

Hilli, his wife and mother-in-law were killed in the shooting Wednesday in a forest car park in a French Alpine tourist area, along with a local cyclist.

Each was shot in the head in a killing that bore many of the hallmarks of a professional assassination and that prosecutors described as an act of "extreme savagery".

Two young daughters of the victims survived, including the four-year-old and her seven-year-old sister, who was seriously injured after being shot in the shoulder during the attack and suffering a fractured skull from what authorities said were "extremely violent" blows to the head.

Maillaud said the older girl had undergone surgery and was doing better.

"She was operated on again, she is doing well," he said. "Her state of health is no longer causing much worry. She is out of danger."

He said the formal request for DNA samples and a search of the family's home was sent to Britain Friday morning.

He said police were hoping to "find certain things in the home that could give us leads on the killers".

Neighbours in England said Hilli was an engineer and identified the other victims as his wife Iqbal, who was carrying an Iraqi passport, and his mother-in-law, who had a Swedish passport. The couple's daughters were named as Zainab, aged seven, and Zeena, aged four.

The victims' bodies and the surviving girls were discovered Wednesday in a forest car park near the village of Chevaline in France's picturesque Haute-Savoie region, which is popular with tourists including many Britons.

Three of the bodies -- a man in the driver's seat and two women in the back -- were found inside a British-registered BMW estate car. The body of the second male victim was lying nearby.

Authorities in France identified the fourth victim, a cyclist who apparently stumbled across the scene by chance, as Sylvain Mollier, a father-of-three who lived in the area and worked in the nuclear industry.

The family had been staying near where they were killed since September 3 at the Saint Jorioz camp site, where fellow campers reported their disappearance on Wednesday.

A veteran of Britain's Royal Air Force who has a second home in the area discovered the victims, having cycled into the car park at 3:48 pm Wednesday.

Several witnesses reported seeing a car speeding away from the scene around the time the attack took place. Investigators believe an automatic pistol was used and 15 spent bullet casings were found in the area.

The killer did not appear to have fired indiscriminately as the bullets had gone only through the windows and not into the body of the car. No weapon was found at the scene.

French President Francois Hollande has vowed that "everything will be done to find the killer or killers."