It comes as an uncle and an aunt of two girls who survived the shooting arrived in France on Friday night.
French police have also asked Italian and Swiss authorities to help them in their hunt for those responsible.
Fifty year old Iraqi-born Saad al-Hilli, his wife Iqbal and his 74-year old mother in law were found dead inside their car at Chevaline, near Lake Annecy, on Wednesday.
A cyclist who apparently stumbled across the shooting was also killed.
The family's seven-year old daughter, Zainab, was seriously injured and remains in an induced coma at Grenoble University Hospital.
The youngest daughter, four-year old Zeena, survived by hiding underneath her dead mother’s skirt, and was not discovered until eight hours after police sealed off the crime scene.
The prosecutor at Annecy, Eric Maillaud, says investigators are no longer questioning the youngest girl, but they hope to speak to Zainab as soon as doctors give them the green light.
“We hope that she can tell us what she saw, give some descriptions, the number of people, men or women, the colour of their skin, clothing…” Maillaud says.
The two girls are under police protection, but it's unclear when their uncle and aunt can visit them.
A British cyclist found the victims and told detectives he saw a green four-wheel drive and a motorbike leaving the scene.
Officers also revealed almost 25 bullet casings were found at the site.
Police are expected to release autopsy results at a fresh news conference on Saturday afternoon.
On the other side of the Channel, four French investigators will join British detectives to search the slain family’s home at Claygate, south of London.
British media reports suggest the house was left to Saad al-Hilli in his mother’s will.
Among several theories, detectives are investigating whether a financial dispute between Saad and his brother led to the shooting.
However, the brother went to police on Thursday to proclaim his innocence and to help with the investigation.
Maillaud says he will be questioned by detectives as a witness.