Annecy prosecutor Eric Maillaud says the man in the artist's impression released today may be responsible for the murders, or a key witness to the Alps murders.
"The motorcyclist who we are trying to find was seen by officials from the National Forestry Office a short time before the murders, and in the proximity of the car park where the murders took place," he said.
"It is completely unknown who he is.
"It could be that he was on a walk and did not see anything; that he is someone who saw something (a witness); or that he is the perpetrator of the murders. All these hypotheses are being considered.
"His helmet is very particular and there are only a few thousand of these models worldwide. The lower part of the helmet opens laterally to reveal the lower face."
A British climber has died after falling 200 metres down a steep slope in the Austrian Alps, local police said.
The 42-year-old man was accompanied by a friend when he lost his balance on rocky terrain in the western province of Tyrol yesterday afternoon.
Police described the pair as "inexperienced climbers" and said that they had been forced to turn back while walking a mountain trail in the Durrach area, because parts of the path were covered in snow.
A police helicopter was used to recover the body of the man, who has still to be named.
A Foreign Office spokeswoman said: "We can confirm the death of a British national in Austria. We are providing consular assistance to the family."
On the border of Austria and Italy, the Zillertal Alps mountain range where the accident took place offers a range of routes for both novice and experienced climbers.
Four British citizens are being treated for serious injuries in hospital in France, a spokesman for Skibound confirmed this evening.
In total, 29 passengers travelling on the coach were hospitalised. The British driver died following the crash.
Twenty nine passengers have been taken to hospitals in the area, four of which are being treated for more serious injuries. The further 23 passengers have escaped injury and are now with police and councillors in a local hotel.
The spokesman said the company was concentrating on repatriating those involved in the accident, the cause of which is still being investigated.