Saad al-Hilli, 50, his wife Iqbal, 47, from Surrey and grandmother Suhaila al-Allaf, 74, who lived in Sweden, were all gunned down in their car on September 5th not far from the town of Annecy. French cyclist Sylvain Mollier, 45, was also killed nearby.
The al-Hilli's two daughters – seven-year-old Zeinab, and four-year-old Zeena – survived the attack.
Detectives, who have so far been unable to find a motive for the murders, had hoped to visit Saad al-Hilli’s home country of Iraq to see whether they could unearth any clues that might lead them to find those responsible for his assassination.
But the French Foreign Ministry in Paris has told investigators that the ongoing security situation in Iraq meant it was too dangerous to sanction their visit, despite prosecutors stressing the need that al-Hilli's background might hold the key to the solving the murders.
Recent reports in the British media claimed that former Iraqi dictator Saddam Hussein had deposited almost €100,000 into al-Hilli’s Swiss bank account.
French authorities had written to their counterparts in Iraq seeking cooperation but when they received no response they decided the best move would be to visit Iraq in person.
Investigators want to understand the reasons why Saad al-Hilli left Iraq in the 1980s, believing it could shed some light on why he was assassinated. But for now that line of inquiry has been “frozen” according to prosecutor in Annecy Eric Maillaud.
Talking earlier this year about the need to go to Iraq Maillaud said: “The aim is to see if we can make a link between the murders and the Iraqi origins of the victims.
“We want to know exactly what Saad al-Hilli’s father did professionally in Iraq, where he got his wealth from and why he left the country.”
The Foreign Office's decision is a blow to investigators who have been under intense pressure to find the killers.
Earlier this month prosecutor Maillaud told The Local that the killers may never be found but that it was too early to give up.
"Of course it is possible we will never find them, but it's too early to conclude that.
"The investigation is only six months old, which in terms of police inquiries is a very short period of time. It's out of the question that we will be thinking like that now," he said.