Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps.An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

A road sign is seen while a Gendarme blocks access to a killing site near Chevaline, French Alps, Wednesday Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps. An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps.An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday, Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps. An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo / Alexis Moro)

Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps.An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps. An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

A Gendarme's car heads to a killing site near Chevaline, French Alps, Wednesday Sept.5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps. An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo/Alexis Moro)

Gendarmes block access to a killing site near Chevaline, French Alps, Wednesday, Sept. 5, 2012. French authorities say at least four people have been shot to death in a forest in the Alps. An official with the regional administration for the Haute-Savoie region says three of the bodies were found in a BMW registered in Britain. (AP Photo / Alexis Moro)

A gendarme blocks access to site where people were shot to death near Chevaline, French Alps, Thursday Sept. 6, 2012. A 4-year-old British girl hid for eight hours beneath the bodies of slain family members in the back of their car before she was discovered by French investigators who had been guarding the vehicle, a prosecutor said Thursday. Three people - a man and two women - had been shot to death, as was a French cyclist whose body was found nearby. (AP Photo/Laurent Cipriani)

A general view of Annecy in the Haute-Savoie region of south-eastern France near where the bodies of four people were found, three family members in their car and another cyclist who also suffered gunshot wounds and was found lying close to the vehicle. A four-year-old British girl was found alive underneath the bodies of her parents around eight hours after a brutal massacre in the Alps, French authorities said today

A general view of Annecy in the Haute-Savoie region of south-eastern France near where the bodies of four people were found, three family members in their car and another cyclist who also suffered gunshot wounds and was found lying close to the vehicle. A four-year-old British girl was found alive underneath the bodies of her parents around eight hours after a brutal massacre in the Alps, French authorities said today

A car drives through the entrance of the campground where the British family were holidaying in Saint Jorioz, near Annecy (AP)

A general view of Annecy in the Haute-Savoie region of south-eastern France near where the bodies of four people were found, three family members in their car and another cyclist who also suffered gunshot wounds and was found lying close to the vehicle. A four-year-old British girl was found alive underneath the bodies of her parents around eight hours after a brutal massacre in the Alps, French authorities said today

Gendarmes guard the camp where the British family were holidaying at Saint Jorioz, near Annecy (AP)

Cameras are seen in front of Gendarmes who blocks access to a site where people were shot to death near Chevaline, French Alps, Thursday Sept. 6, 2012. A 4-year-old British girl hid for eight hours beneath the bodies of slain family members in the back of their car before she was discovered by French investigators who had been guarding the vehicle, a prosecutor said Thursday. Three people - a man and two women - had been shot to death, as was a French cyclist whose body was found nearby

CLAYGATE, ENGLAND - SEPTEMBER 06: Journalists gather at a house believed to be owned by a British family murdered in a shooting in the French Alps France on September 6, 2012 in Claygate, England. French police are investigating a multiple murder after the bodies of three members of a British family were found in a bullet-riddled car in the French resort of Annecy. A 4-year-old girl, who had remained hidden for hours, was also found alive after investigators eventually entered the car. Local news agencies have named the male victim as Saad al-Hilli. (Photo by Peter Macdiarmid/Getty Images)

A gendarme blocks access to the site where four people were shot dead near Chevaline in the French Alps (AP)

Police tape seals the caravan and tent used by Saad al-Hilli and his family while on holiday at the Le Solitaire du Lac campsite on Lake Annecy in the Haute-Savoie region of south-eastern France. Mr Al Hilli, his wife Iqbal and his mother-in-law were found murdered in their BMW car near the village of Chevaline on Wednesday. PRESS ASSOCIATION Photo. Picture date: Tuesday September 4, 2012. One of his daughters was injured and a second lay undetected and uninjured for hours in the back of the vehicle. A French cyclist was also killed in the attack possibly killed after discovering the crime in progress. See PA story POLIDE Alps. Photo credit should read: Chris Ison/PA Wire

The caravan and tent used by Saad al-Hilli and his family while on holiday at the Le Solitaire du Lac campsite on Lake Annecy in the Haute-Savoie region of south-eastern France.

The caravan and tent used by Saad al-Hilli and his family while on holiday at the Le Solitaire du Lac campsite on Lake Annecy in the Haute-Savoie region of south-eastern France.

The property in Surrey is being searched in a bid for clues in the probe into the shootings

French and British police have begun a detailed search of the home of the couple gunned down in the Alps after it emerged all four people who died were shot twice in the head.

Saad al-Hilli, 50, was killed in his car alongside his dentist wife, named by neighbours as Iqbal, on Wednesday.

An older Swedish woman travelling in the car also died in the shooting, along with Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack in Chevaline.

The couple's four-year-old daughter Zeena lay undiscovered under her mother's corpse for eight hours after the murders, while her seven-year-old sister Zainab remains in a medically induced coma after being shot and beaten.

Post-mortem examinations revealed each of the victims killed in the attack had been shot a number of times, including two hits to the head, public prosecutor Eric Maillaud said.

Police entered the al-Hillis' family home in Claygate, Surrey, as a team of four French officers arrived in the UK. The caravan in which the family had been staying at the Le Solitaire du Lac campsite in Saint-Jorioz was also examined by police. French authorities have now asked their Italian and Swiss counterparts to help the investigation.

Surrey Police erected a tent at the front of the al-Hillis' home as they prepared to conduct a search of the property with the French police team, led by Colonel Marc de Tarle. Two French detectives entered the house with two British officers, followed by scenes of crimes officers in full protective suits.

Families have been visiting the home to leave floral tributes outside, along with teddy bears and a Mr Men 'Little Miss Trouble' book.

Two relatives of the al-Hilli family have travelled to France, alongside a British social worker, and will visit the girls who are under police supervision. However it was unclear when they would be able to see the elder girl, Zainab, as she continues to be treated in hospital.

Police plan to look at aspects of Mr al-Hilli's life to try to find a motive for the murders and also speak with his brother, named in reports as Zaid Hilli. Investigators said Mr al-Hilli's brother approached UK police to deny any feud with his sibling over money. Mr Mauillard said the brother would be interviewed along with the rest of the al-Hilli family.

PA