The team plan to search his house in Claygate, south-west London, it was announced yesterday.
Investigators also revealed Mr al Hilli’s brother has denied any family feud with his sibling over money.
French officer Marc de Tarle is in Britain and he will be joined by three colleagues over the next 24 hours or so.
Iraqi-born Mr al Hilli, 50, was gunned down in his car alongside his dentist wife, named by neighbours as Iqbal, while on holiday in the Alps. An older Swedish woman, who was travelling in the car, was also killed, along with Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack.
The couple’s daughter Zeena, 4, lay undiscovered under her mother’s corpse for eight hours after the murders, while her sister Zainab, 7, remains in a medically-induced coma after being shot and beaten.
French prosecutor Eric Maillaud said yesterday that investigators were told of a possible feud between Mr al Hilli and his brother over money, but he said the sibling denied the row.
Mr Maillaud said Mr al Hilli’s brother told police: “No, I don’t have a conflict with my brother.”
Police plan to search Mr al Hilli’s house and look at other aspects of his life in a bid to find a motive for the murders. “Up until now the police in Britain were guaranteeing the safety of the house but now it’s a Franco-British inquiry that is starting and we can now enter the house of Mr al Hilli,” said Mr Maillaud.
“We’ve only guaranteed in the last few hours that it’s Mr al Hilli. His life, his job — I heard that he was the owner of three companies — all of that is the sort of thing that we have to find out about in England and the investigator has just landed.”
The four-year-old girl has spoken to police and confirmed that two of the victims were her parents, but said she did not know the Swedish woman very well. The prosecutor said: “The little girl said, talking like a little girl does, she didn’t know [the Swedish woman] very well. We have to assess very clearly, who was that lady with the Swedish passport?”
He said the girl remained under the care of psychiatric teams and had spoken about what he described as the “terror” of what happened, but did not see anything because she was hiding.
Her sister is not yet well enough to be interviewed but it is hoped she will be able to provide vital details of the attackers.
Witnesses have said they saw a green 4x4 in the area at the time of the killings, and possibly a motorbike.
All the victims were shot at least three times and 25 spent bullet cartridges were found at the scene.
Mr Maillaud said it was not the first time the family had been to the campsite where they died.
One theory is shots could have been fired during a bungled armed robbery, with Mr Mollier being a witness to the crime. Some reports have suggested Mr al Hilli — an engineer who left Iraq several years ago — was put under surveillance by Metropolitan Police Special Branch during the Second Gulf War.
A spokesman for Scotland Yard would not comment. It is understood there is no link between the deaths and any national security issues.