"The weapon used in the crime has not been found, nor has the motorcycle helmet on the identikit picture, nor has the motorbike described by several witnesses and sought by investigators, so the inquiry continues," Annecy prosecutor Eric Maillaud told reporters on Friday.
The man, Eric D, will be questioned again in relation to an "illegal trade in weapons and munitions found during searches", he said.
Another man has been detained in the connection and charges may include gangsterism.
The man's lawyer, Marc Dufour, said his client was "shaken" by his detention and the publicity it has attracted.
"When you take a close look at his movements he couldn't have been at the scene of the crime in the time needed," he said.
The man was to be went to court when his detention was over and a new inquiry was to be opened.