Two French officials said authorities were working to confirm the identity of the recipient, but were not able to immediately confirm media reports that it was sent to an unspecified person in Syria.
Yesterday, key suspect Yassine Salhi allegedly crashed a truck into an US-owned chemical warehouse and hung his employer's severed head on a factory gate in Saint-Quentin-Fallavier in what authorities are calling a terror attack.
He was arrested and remained in police custody today.