The motive behind the brutally cold-blooded massacre of three members of a British family on holiday, and of a cyclist who was out for a stroll, has been murky since the killings last Wednesday. But a little girl in a French hospital could soon change all that.
In a hospital guarded by armed police in the French alpine town of Grenoble, the relatives of a seven-year-old girl are waiting for the right moment to break the terrible news that her parents are dead.
With her relatives at her bedside, Zainab Al Hilli is perhaps the only witness to the brutal killings of her mother, father and grandmother in a wooded beauty spot near the picturesque Lake Annecy.
Her four-year-old sister Zeena also survived the massacre, but only by hiding, mute with terror for eight hours, under the skirts of her dead mother in the family car.
That two little girls have lost their parents under the most brutal of circumstances remains almost the only certain fact nearly six days after a British cyclist stumbled across the scene of slaughter.
The mystery of who killed Saeed Al Hilli, his wife Iqbal and his elderly mother-in-law deepened yesterday as police searching the family home in Surrey, England evacuated neighbours and called in the bomb squad, revealing that a "potentially explosive substance" had been found.
Officers from the Royal Logistics Corps bomb disposal squad spent two hours at the property, without revealing what had been found.
Since the weekend, the investigation into the murders has taken on an international dimension, as British police collaborate with French detectives, and with reports that the Swiss authorities are also now involved.
In the absence of a named suspect - or any suspects - speculation about the motive for the killings has ranged from a family feud to a contact killing ordered to silence Mr Al Hilli over his work in the satellite industry.
There seems little doubt, though, that Al Hilli, 50, was the main target, and that the other killings, including that of a passing French recreational cyclist whose wife had recently given birth, were collateral damage.
Born in Iraq, Al Hilli moved to Britain in the 1970s after his father fell out with the ruling Baath party. The teenager was educated in London and trained as a mechanical engineer in the aerospace industry. In 2002 he took British citizenship.
He is understood to have met his dentist wife on a holiday in Dubai 10 years ago, with the couple raising their daughters in Claygate, an archetypal suburb of mock-Tudor houses to the south of London.
At the time of his death, Al Hilli was working for Surrey Satellites Technology Limited, a private space engineering company whose work is mostly in civilian communications and environmental monitoring.
In the immediate aftermath of the killings, suspicion fell on the dead man's elder brother Zaid amid allegations of a family feud over an inheritance.
The two men were said to have fought over their father's estate after his death in Spain last year. Al Hilli had written to a friend, saying he had cut himself off from Zaid, 53, for "underhand things" involving their late father's assets.
In the letter to the friend, he complained: "Zaid and I do not communicate any more as he is another control freak and tried a lot of underhand things, even when my father was alive."
For his part, Zaid Al Hilli has denied any problems with his brother, with a cousin insisting that Zaid was in "very deep shock" and "clearly devastated" by the killings.
A second theory involved alleged links between Saad Al Hilli and the defence industry, with newspaper reports in Britain suggesting he had been working on a "secret project" linked to a company making "eye in the sky" satellites. It was unclear, however, why this would make him a target for murder.
Those who knew the family well find it hard to believe Al Hilli could have been involved in anything that might result in assassination.
Friends and neighbours described a loving husband, devoted to his daughters. He was "the perfect father and a wonderful engineer", one former colleague told The Daily Telegraph newspaper.
A neighbour, George Aicolina, described the "stunning little girls with lovely eyes", adding "they were a very happy and caring family."
At the same time, there were suggestions of a darker side to the family's apparently idyllic life in suburbia. Another neighbour, Philip Murphy, told the Daily Mail that he believed Al Hilli had been under surveillance by intelligence officers from the British Special Branch and that police had asked if they could use his driveway to watch the house.
"They would sit there all day in their parked car just looking at the house," Mr Murphy claimed, adding that the surveillance began at around the time of the invasion of Iraq by American and British forces in 2003.
Jack Saltman, another neighbour, said he had been told something by Al Hilli over the garden fence that he would be passing on the investigating police. "It was something Saad said to me before he went but at this stage I do not feel I can disclose that, but I will tell the police exactly what he told me before he left," Mr Saltman said.
If the murders were a professional hit, they were carried out with meticulous and cold-blooded brutality. Yet at the same time, it is not clear why Zainab was not killed along with her family or whether the French cyclist was anything more than someone in the wrong place at the wrong time.
Al Hilli and his family, including his mother-in-law, who holds Swedish nationality, had set out from England on camping holiday in the Haute-Savoie, driving through France in their maroon BMW estate car, caravan in tow, and arriving at a campsite near Saint Jorioz, a village on the western shore of the lake.
Last Thursday, the family drove down a narrow track in forested area popular with holidaymakers near the village of Chavaline south of the lake. The alarm was raised by a former British Royal Air Force servicemen, now living in the area, who found Zaineb staggering towards him, beaten about the head and shot in the shoulder.
Inside the vehicle were the bodies of her parents and 74-year-old grandmother, Suhailia Al Allaf. Each had been clinically shot twice through head, probably with a semi-automatic pistol. It was only after questioning holidaymakers at the campsite that police realised there were two children. Hidden for eight hours, undetected even by thermal imagining, Zeena was found still alive inside the BMW.
Police say she cannot provide any information about the attack. Yesterday sources close to French police were quoted as saying that the weapon was "an average calibre considered old by the experts and not consistent with modern firearms" and reporting that only one gunman was involved. Nor have they ruled out the possibility that the family accidentally stumbled across some form of criminal activity and was killed to silence them.
Such were the injuries inflicted on Zainab that doctors placed her in an induced coma from which she has only now emerged. The task now is to break the news of her parent's death while attempting to discover if the little girl who saw too much also knows enough to put police on the trail of the killer.