LONDON (CNN) -- Investigators identified two of four people Friday who died in a mysterious attack in the foothills of the Alps this week.
They also said a witness reported seeing a green 4x4 vehicle and a motorbike near the site of the killings, in a mountainous and wealthy area of eastern France.
British nationals Saad al-Hilli and his wife were among three people whose bodies were found in a car, shot to death in a secluded parking lot, French prosecutor Eric Maillaud said. The identity of a third person who was killed in the car is not yet clear.
The fourth victim, French cyclist Sylvain Mollier, was found with a gunshot to the head in the same parking lot off a forested road, near the village of Chevaline.
The identities of those in the car were confirmed by al-Hilli's 4-year-old daughter, who spent several hours in the vehicle, apparently immobilized by fear, Maillaud said. Her 7-year-old sister was found, severely injured, outside the car. She is under medical protection and cannot yet be spoken to.
A British cyclist who was the first to discover the bodies near Annecy, meanwhile, told police he saw a green 4x4 vehicle and a motorbike near the site of the killings, the prosecutor said. The witness, who is a former serviceman, did not hear anything but pointed out to police that he was carrying out strenuous activity, Maillaud said. The prosecutor said 4x4 vehicles are not unusual in the area.
Maillaud has opened a judicial investigation for murder and attempted murder in the case, Joelle Robert of the Annecy prosecutor's office told CNN.
Maillaud said autopsies would be carried out Friday. The results are expected later Friday or Saturday morning, CNN affiliate BFM-TV reported.
The grisly case has captured headlines in France and Britain, sparking wide speculation about possible motives for the killings, from a family feud to a drug deal gone wrong.
Al-Hilli's brother went to the police voluntarily after learning from the media that his relatives had been shot to find out what had happened, Maillaud said. He told police there had been no conflict with his dead brother, as had been reported, Maillaud said.
French authorities have said they are ruling nothing out in their investigation into what Maillaud described as an act of "extreme savagery."
French and British news reports have identified al-Hilli as an Iraqi-born engineer who lived in Claygate in Surrey, south of London, with his wife and two daughters.
Surrey Police have said they are helping police in Annecy with their investigation into the killings, though they haven't given further details. Officers from Surrey Police were stationed Thursday outside the house identified by neighbors as that of al-Hilli.
Neighbor Jack Saltman, whose home backs onto the family's garden, said al-Hilli and his wife had come from Iraq "many years" ago and both spoke "perfect English."
"They were a delightful family," Saltman said.
The neighbor said al-Hilli's wife, Iqbal, was a dentist and that the two daughters were "absolutely beautiful." He had been asked to keep an eye on the house while his neighbors were away in France, Saltman said.
An accountant for Saad al-Hilli, Julian Stedman, said the engineer had at least one business registered locally.
British Prime Minister David Cameron said he and French President Francois Hollande discussed the "terrible killings of ... the British family" during a meeting Thursday in London.
He promised British authorities will cooperate "very closely with the French authorities" to "help those poor children" and "get to the bottom of what happened in this clearly very tragic and awful case."
"Both a French and a British family have been impacted by this terrible event, and we will do our utmost to identify the perpetrators," added Hollande in a joint news conference after the two leaders' meeting.
The gory scene was discovered Wednesday afternoon by a passing cyclist, a retired British serviceman who has not been named.
After helping the injured girl, who was near the car, he alerted emergency services.
The younger girl had spent nearly eight hours inside the car with the three corpses before French police, who were waiting for forensic experts to arrive before opening the vehicle, were made aware of her likely presence and discovered her hiding under the legs of one of the women.
Multiple bullet casings surrounded the BMW when authorities came upon it, with bullet holes piercing its windows but none in the body of the car, according to Maillaud.
The driver and an older woman found dead in the car had been shot in the head, the prosecutor said Thursday, "and it was obvious that (whoever) did this wanted to kill."
The car was registered to a man with an Iraqi passport who was a naturalized British citizen and had lived in Britain since at least 2002, he said. The passport was used when the visitors checked in to the campsite where they were staying, Maillaud said, but police can't yet confirm whether it belonged to the man who was found dead in the car.
The man named in the passport was born in 1962, the French prosecutor said. A Swedish passport found by investigators may belong to the older woman, he added. The victims are believed to be British nationals but may have held dual citizenship.
Swedish Foreign Ministry spokeswoman Catarina Axelsson described "the French information about the Swedish national (as) reliable," adding that authorities there were awaiting a "final confirmation of the identity."