Detectives probing a massacre in the French Alps have identified the type of weapon used in the horrifying attack.
Police are also combing through security camera footage in an attempt to identify the escape route taken, in an investigation that has thrown up more questions than answers.
As the inquiry grows in complexity -- the victims had direct links to four different countries -- police in southeastern France have still been unable to trace a dark-coloured 4x4 vehicle spotted near the crime scene.
Officers have also searched woodland and remote hikers' huts for any trace of the killer.
An unnamed British man who alerted police to the shootings is said to have seen a car, and a motorcycle a few minutes later.
A source close to the probe told AFP that only one weapon, a 7.65mm automatic pistol, was used to kill three members of a British-Iraqi family and a passing French cyclist on September 5 but Annecy prosecutor Eric Maillaud would not confirm this late Monday.
Progress on other fronts stalled however with one of the child survivors of the attack still unable to talk to investigators and the suspected discovery of explosives at the family's home near London turning out to be a false alarm.
The revelation about the type of gun used to fire two bullets into the heads of each of the victims followed initial analysis of 25 spent cartridges discovered at the scene of the murder and bullets retrieved from the corpses.
The high number of cartridges found had led to speculation that there might have been more than one shooter.
The 7.65mm calibre is one used in a range of "relatively old, even outdated", medium calibre pistols which are easy to conceal, according to Yves Gollety, the president of France's Chamber of Gunsmiths.
It has been used for automatic pistols including the Walther PP, widely used by police forces around the world, and the Mauser, developed for Germany's armed forces.
It was also used for Unic model issued to French police in the 1950s and 1960s and numerous weapons manufactured in the former communist states of eastern Europe, Gollety said.
Forensic specialists are able to establish whether different bullets came from the same gun by microscopic comparison of traces created by their passage through the barrel of the weapon.
This ballistic fingerprint may also help investigators establish where the bullets came from and whether the pistol had been used in other crimes.
Annecy prosecutor Maillaud said in a statement to AFP that "in contrast to allegations by a large number of media the Annecy prosecutor firmly denies that he has confirmed the nature, calibre and number of weapons used in the Chevaline killings".
Police in Claygate on the outskirts of London spent a third day searching the home of shooting victims Saad and Ikbal al-Hilli and a major development appeared imminent when British army bomb disposal experts were called to the house and neighbouring properties were evacuated.
After several hours of tension, it was announced that nothing hazardous had been discovered.
With the motive for the killing still a mystery, investigators are pinning a lot of hope on testimony they hope to receive from the Hilli's daughter Zainab.
The seven-year-old survived the attack along with four-year-old sister Zeena but remained under sedation Monday as she recovers from a fractured skull and a bullet wound in the shoulder.
"When the doctors give us authorisation we will be able to interview her in hospital but for the moment they are not allowing it," Maillaud told AFP earlier.
"She was in an induced coma which she was brought out of on Sunday but she remains under sedation."
Zeena survived the attack unscathed after hiding in the back of the family car but has not been able to provide any significant information. She returned to Britain on Sunday with relatives.