London (CNN) -- A French prosecutor and magistrate working on the investigation into the murder of four people in the French Alps last week are to travel to London on Thursday to meet with British authorities.
Prosecutor Eric Maillaud said Wednesday that he and Judge Michel Mollin would arrive in London on Thursday morning and stay until the next day.
The trip is intended to help overcome "difficulties" relating to the two countries' different languages and legal systems, he said. They will join a handful of French investigators already working with local police in Britain.
Two of those killed in the brutal shooting, Saad and Ikbal al-Hilli, lived in the well-heeled town of Claygate, located south of London in the county of Surrey.
They were found last Wednesday shot to death in a car near France's Lake Annecy, along with Ikbal al-Hilli's 74-year-old mother. The al-Hillis' two daughters survived, one with wounds from a beating and a gunshot.
Ahmed Al-Saffar, an uncle of Ikbal al-Hilli, said Wednesday that the family, which he described as being of Iraqi-Arabic origin, was "heartbroken by this shocking crime."
"We are very grateful for the support provided by the British, French and Iraqi authorities during this difficult time," he said, in a statement released on his behalf by the UK Foreign Office.
"We hope that those responsible for the deaths of our loved ones are brought swiftly to justice."
French authorities agreed late Wednesday to release the bodies of the girls' parents and grandmother, along with that of the fourth victim, a French cyclist, to their respective families, Maillaud said.
The elder sister, named in media reports as Zainab, is still recovering from her injuries and investigators have not yet been able to question her, he said.
The girl is also being protected by police in case of a further threat to her safety. She came out of a medically induced coma Sunday, the French prosecutor's office said.
Investigators in France were requestioning witnesses Wednesday, a week after the attack, and have sealed off the crime scene again as they attempt to piece together the sequence of events.
Witnesses have given different reports concerning vehicles seen in the area, which investigators are attempting to resolve, Maillaud said.
Authorities have been tight-lipped about possible perpetrators and motives in the attack, although speculation has been rife in the British media.
But Maillaud confirmed that investigators are focused on three main areas in what is a complex inquiry.
One involves a reported family dispute over money, involving Saad al-Hilli's brother, he said. The prosecutor said he and Mollin did not intend to interview the brother while in Britain, however.
The second area for investigation is Saad al-Hilli's job, and the third is his links to his native Iraq, Maillaud said.
Born in Baghdad in 1962, Saad al-Hilli was a naturalized British citizen who had lived in the United Kingdom for decades.
He was an engineer working at Surrey Satellite Technology, a high-tech company owned by EADS, an aerospace corporation that builds satellites.
"The fact that he was born in Iraq, that he had family in Iraq, of course that's something that is of interest and we are asking ourselves if there is a link between that and his death," said Maillaud.
He said investigators hoped to find a significant number of clues in Britain.
British officers have been searching for information at the al-Hillis' home in Claygate since the weekend, in cooperation with the visiting French investigators.
The Surrey police department said Wednesday it is "continuing to provide all possible support, including the provision of specialist search teams" at the Claygate address.
The force has also provided officers to work with the families of the victims, the police statement said.
Maillaud called last week's attack on the al-Hilli family an "unheard-of savagery."
The French cyclist, Sylvain Mollier, was killed alongside the British-Iraqi family members on the outskirts of Chevaline, an Alpine village near the picturesque Lake Annecy that is popular with outdoor enthusiasts.
Each victim had two gunshot wounds to the head.
While the couple's 7-year-old daughter was badly beaten and shot, their 4-year-old daughter was unharmed. She hid for hours behind her dead mother's legs before she was found by police.
CNN's Stephanie Halasz contributed to this report.