French investigators in the Alps were poring over the movements and contacts of a 34-year-old former military dog handler on Thursday to look for possible links to a series of unsolved missing person cases in the region.

Nordahl Lelandais was charged Wednesday with killing a hitchhiking soldier in April, having already been accused over the abduction of a nine-year-old girl at a wedding in August.

The federal prosecutor in the local town of Chambery, a gateway to the snowcapped Alps, said Wednesday that "all of the worrying disappearances" in the region would be reexamined.

These are expected to include the case of 24-year-old Belgian chef Adrien Mourialme who was working in a high-end restaurant on the banks of the picturesque Lake Annecy before he went missing in early July.

In 2011, another man disappeared at the Elements electronic music festival near the Albertville ski resort and a second partygoer went missing at the same event the year after, French media reported.

Reports suggested investigators might also re-examine a famously unsolved murder case near the Alpine village of Chevaline in 2012 when a British-Iraqi family and a cyclist were gunned down in broad daylight.

No motive has been found by police despite exhaustive investigations in Britain, France and Iraq.

A legal source, speaking to AFP on condition of anonymity, said "for the moment, there is nothing to indicate any involvement at all" of Lelandais.

- 'Not a delinquent' -

The cases of 24-year-old missing soldier Arthur Noyer and the disappeared girl, named Maelys de Araujo, have captivated France and were front-page news again Thursday as reporters raked over Lelandais' background.

He has denied all charges against him, either replying calmly to questions while in custody or simply refusing to respond to allegations put to him by investigators.

The skull of the missing soldier was discovered by a hiker in early September, while Maelys' body has not been found despite intensive efforts by hundreds of police, backed by dogs and helicopters, as well as volunteers.

She went missing at around 3:00 am at a wedding in August where Lelandais was a guest of the groom.

The suspect is an unmarried dog lover with no long-term job who drove a black Audi, which has emerged as a crucial piece of evidence allegedly tying him to both murder cases.

The former military man lived with his parents in the village of Domessin and was found by investigators to be a frequent watcher of pornography.

Several women who say they are ex-girlfriends have also come forward to complain about sexually explicit videos he posted of them online.

Analysing his internet searches, investigators found that the martial arts fan and occasional cocaine user had looked up "decomposition of a human body" after the soldier's disappearance.

His lawyer, Alain Jakubowicz, has blasted police and prosecutors investigating the Maelys case for leaking damaging information against his client, while Lelandais' mother has also leapt to his defence.

"He did a few stupid things when he was younger but he's not a delinquent, he's a nice young man. He's not someone who's aggressive, you can ask the neighbours," she told the LCI news channel in September.

The French army has refused to comment to AFP about allegations in the media that he was discharged in 2005 after four years of service because of psychological problems and drug use.

Lelandais, born in Paris, was also convicted for an arson attack on a restaurant in the Alps region in 2009, a crime which he denied.

During interviews about the murder cases, he has been "calm, cold, collected," one source close to the case told AFP, while another talked about him as a "Jekyll and Hyde" character.

Some witnesses have testified that he is a slightly withdrawn but gentle character, while others have spoken about someone who could be violent and aggressive, sources close to the case told AFP.