Investigators are hoping the seven-year-old British girl who survived the shooting of three members of her family will provide the key to solving the killings.
Iraqi-born Saad al-Hilli, 50, was gunned down in his car alongside his dentist wife, named by neighbours as Iqbal, and a woman believed to be her mother.
The couple's children, four-year-old Zeena and Zainab, seven, are apparently the only witnesses to the shootings on an isolated French Alpine road and are now under police protection.
Investigators are waiting for the green light from medical staff at Grenoble University Hospital to talk to Zainab as the motive behind the killings remains a mystery.
Annecy prosecutor Eric Maillaud said detectives hope the youngster, who is in a stable condition, will recover sufficiently from the trauma to speak to them and that her memory was not damaged.
Mr Maillaud said: "We are waiting for the ballistic team's report and, when possible, a hearing with the eldest girl.
"Maybe she can give us information on the number of people present, for example, or the colour of their skin, and other elements of description that might allow us to consider a bit more seriously a first lead. Medical staff have not yet given us access to the girl, we are waiting for their decision."
Zainab was beaten repeatedly around the head and shot in the shoulder in the attack on the family from Claygate, Surrey, which took place on Wednesday. She was hit with "tremendous ferocity", said the prosecutor.
Her younger sister was found alive in the BMW estate underneath the bodies of her relatives about eight hours after the massacre, which also saw a passing French cyclist, Sylvain Mollier, 45, shot dead.
Mr Maillaud said he did not expect the four-year-old to be able to help police. He added: "She is a little girl who was hidden. It's not her who will help us progress the inquiry."