A police search operation has taken place at the Surrey home of a British man shot dead in the French Alps along with his wife and two others.
Two French officers, accompanied by Surrey Police, began examining the home of Saad al-Hilli, 50, in Claygate.
They have also asked Italian and Swiss counterparts to help them in their hunt for those responsible.
Post-mortem tests showed all those killed were shot twice in the head, French prosecutor Eric Maillaud said.
Mr Maillaud told a news conference at Annecy near to the site of Wednesday's killings that examinations were completed on Friday night, but refused to go into any more detail.
Meanwhile, speaking outside Surrey Police headquarters, Colonel Marc de Tarle, who heads the National Gendarmerie Criminal Affairs Bureau, said the investigation was likely to be "long and complex" and thanked the force for its support.
Two relatives have gone to France to comfort Mr al-Hilli's daughters, who remain in hospital, and are under police protection.
The man and woman arrived in France on Friday night, accompanied by a British social worker and family-liaison officers from Surrey Police, and are expected to see four-year-old Zeena later.
Zeena spent eight hours hiding in the car before being found by officers.
Police said she was between her mother and the older woman, and hid under her mother's skirt when the shooting started.
Her sister, seven-year-old Zainab, remains in a medically-induced coma in Grenoble University Hospital after being shot and beaten.
The BBC's Imogen Foulkes, in Annecy, said: "Police say they hope a visit will take place soon, but add that any contact must be in the presence of French investigators - a reminder that the al-Hilli family itself is part of their inquiry."
Mr Maillaud told reporters Zeena had been interviewed but he did not see a "need" to speak to her again as she "did not see anything" after taking shelter at her mother's feet.
On Friday, he said Zeena had identified her family and described the "fury" and "terror" of the attack to police.
Mr Maillaud, who had previously said 25 shots were fired in total, told reporters officers had discovered more information about the ballistics but details would not be disclosed publicly.
Earlier media reports said that a possible dispute over money between Mr al-Hilli and his brother, Zaid, is one of the lines of inquiry in the investigation.
Zaid al-Hilli, who had told UK police there was no dispute over "financial matters", would be interviewed by French officers "just like any other family member" as a "witness", Mr Maillaud said.
The prosecutor added a "considerable amount of information" had been gathered and the investigating was fast moving.
He said: "There are 40 French who are working on this matter.... there are a great number of people working on it on the British side... No scenario, no path in fact is closed until you're sure."
The shootings took place near the popular tourist destination of Lake Annecy.
The search of the al-Hilli home is part of efforts to gather background information about the family.
The BBC understands the house was originally owned by Saad al-Hilli's parents and later left to him by his mother in her will.
Floral tributes from neighbours continued to be placed at the property during the day.
Officers from Surrey Police set up a forensic evidence tent in front of the house and gathered evidence outside ahead of the arrival of the French officers.
They spent nearly an hour inside the property and are expected to return later to conduct further searches.
Mr al-Hilli's wife, Iqbal, and a woman thought to be his 74-year-old mother-in-law who held a Swedish passport, were killed during the attack.
The fourth victim, a cyclist whose body was found near the car, has been named as 45-year-old Sylvain Mollier.
The older sister, Zainab, was found close to the car by a British cyclist who discovered the murder scene and alerted the authorities.
The BBC's Mark Lowen, in Annecy, said: "Prosecutors hope that if she recovers, she may provide the key to what happened here in this tranquil corner of France, and who is to blame."
They are looking into reports of a green or dark-coloured four-wheel drive vehicle and a motorcycle, apparently seen by the cyclist who discovered the murder scene. But they have pointed out that such vehicles were common during the tourist season in a mountainous region.