The accused face charges of murder and criminal association over the January 6 killings in the forest of Bayotte.
The 16 suspects, who were arrested on Sunday, also face charges of participation in a rebel movement and possession of weapons without authorisation, according to the source.
Six other people detained by police have been released without charge “for the moment”, added the source without naming the suspects.
The victims were looking for firewood, according to friends who escaped and their families.
But several sources told AFP the group was potentially involved in the illegal logging trade in a region with plentiful rosewood and teak, both highly prized in China.
Casamance is separated from the rest of Senegal by The Gambia and has been the target of an independence campaign for more than 35 years.
A local rebel group, the Casamance Movement of Democratic Forces (MFDC), was initially fingered for involvement in the killings but has strongly denied the allegations.
It says the logging network is run by corrupt local military and governmental officials, and that the murders were linked sawmill operators who work secretly in the forest.
President Macky Sall has suspended all authorisation for logging and ordered an overhaul of Senegal’s forestry laws.
Several young members of a village foresty monitoring committee, who were among the men arrested on Sunday, were previously sentenced and then freed in October following a conflict with loggers.
