PARIS — Two arrests in southern France on Tuesday bolstered long-simmering suspicions that the country’s worst terrorist killings in years involved multiple players and were not the work of a ‘‘lone-wolf’’ radical Islamist.

The attacks in March around the southern city of Toulouse left seven dead — including Jewish schoolchildren and French paratroopers — and terrified France. Lawyers for the victims’ families hailed Tuesday’s arrests as a sign of progress in the investigation.