The case is "not cleared up", Annecy prosecutor Eric Maillaud told a press conference on Wednesday, adding that it is "unlikely" that the former police officer will be charged for the murder of Saad al-Hilli, his wife Iqbal, her 74-year-old mother and French cyclist Sylvain Mollier because "there is no apparent link" between him and the killings.
But a friend of the man has been arrested after "trying to flee" and the two may be charged with arms trafficking, which carries a sentence of up to 10 years in prison.
A number of weapons were found at the detained man's home when he was arrested and police were also seen digging up part of his garden.
A motorbike was also seized.
Investigators say the arrested man bore a strong resemblance to an identikit image released in November of a mysterious motorcyclist seen near where the quadruple murder occurred.
There will be more arrests, Maillaud assured the media.