Presumptively, if not yet positively ID’d as, Islamic Jihadists
While the perps may be Muslims, I wouldn’t assume that it is Jihadists. Without knowing more details, it feels like a gang hit at first glance. Marseille is infested with organized crime.
Jihadists are looking for mass killing, driving a big truck through a crowd (as in Nice) is more cost effective for them. When they do use firearms, as in Paris, San Bernardino, and Orlando, they go for big crowds and a high body count.
With France’s embrace of Mohammedism, there’s no shortage of willing hitmen.