Police are to look into whether a suspected serial killer could be behind the unsolved Alps murders in which a British man, his wife and mother-in-law were killed in a forest car park.

Saad al-Hilli, Iqbal al-Hilli and her mother Suhaila al-Allaf were shot dead on holiday in Chevaline, near Annecy, in September 2012, along with a passing French cyclist, Sylvain Mollier.

Despite a massive manhunt, the investigation has all-but petered out.

Police are now questioning a 34-year-old ex-soldier who is the main suspect in two other cases in the area.

One relates to the disappearance of a nine-year-old girl in August at a wedding where the suspect was a guest, the other to the killing of a hitchhiking soldier in April.