The main suspect in the beheading of a businessman took a “selfie” with the slain victim and sent the image to a Canadian mobile phone number, officials said.
French investigators were working to determine the recipient's identity, but were not able to confirm reports that it was an unspecified person now in Syria, where the radical Islamic State group has seized territory.
The main suspect Yassine Salhi, a truck driver with a history of radical Islamic ties, as well as his sister and wife remained in police custody in the city of Lyon, a day after he allegedly crashed a truck into a US-owned chemical warehouse and hung his employer's severed head on a factory gate, officials said.
One of the officials said the image was forwarded via WhatsApp to a phone number in Canada.
The severed head appeared to mimic Islamic State’s practice of beheading prisoners and displaying their heads for all to see, and came days after militants urged attacks during the Muslim holy month of Ramadan. French authorities say Salhi had links to radical Salafists in the past.
Paris prosecutor’s office spokeswoman Agnes Thibault-Lecuivre said the leading suspect has begun to speak to investigators after first refusing to do so.
The site of the beheading wasn’t yet known to investigators, and the victim had been strangled beforehand, she said.
A fourth person arrested on Friday was released without charge. Under French anti-terrorism laws, Salhi and the women can be held up to four days before either being released or facing preliminary charges.
President Francois Hollande’s office said he will convene a meeting with top parliamentary leaders about the matter on Tuesday.
Earlier hundreds turned out in the region to honour the slain businessman Herve Cornara and denounce the violence. Dozens turned out for a minute of silence in Saint-Quentin-Fallavier, the town south-east of Lyon where Friday's attack took place at an Air Products chemicals warehouse.
Several hundred people also gathered outside a housing project in the town of Fontaines-sur-Saone to honour Mr Cornara (54) the manager of a transportation company that had employed Salhi since March. They recalled a kind, humble man who was active in the community of the Lyon suburb.