The macabre picture of Yassin Salhi and the severed head was sent via the WhatsApp messaging service to a number in Canada but authorities had said Saturday that the number could be a relay for a recipient elsewhere.
Authorities were convinced that the final recipient would be in Iraq or Syria, where hundreds of people from France have gone to wage jihad.
Yassin Salhi, 35, “has also given details about the circumstances” surrounding the killing, according to sources close to the investigation, without offering further details.
Salhi left the police headquarters in France’s southern city of Lyon in a van escorted by nine unmarked cars en route to Paris where he will be grilled by specialist officers.
The convoy stopped briefly at Salhi’s house to pick up his passport, where several masked officers bundled him into his apartment, covering his face with a white cloth and fitting him with a bulletproof vest.
His confession came after it emerged the married father-of-three sent a gruesome selfie photo of himself and the severed head to a WhatsApp number in Canada.
Investigators have warned however that it could be a relay number and the intended recipient could be anywhere in the world.
After several hours of silence, Salhi has begun to open up to investigators about the assault, which came six months after 17 were killed in Islamist attacks in Paris that began with the massacre at the satirical magazine Charlie Hebdo.
His wife and sister, who were both taken into custody on Friday, were released.
On Friday morning, Salhi rammed his van into the US-owned Air Products factory near France’s second city of Lyon in what President Francois Hollande said was a “terrorist” attack designed to blow up the whole building.
He was overpowered by a firefighter as he was trying to prise open a bottle of acetone in an apparent suicidal bid to destroy the factory.
Police then made the grisly discovery of the severed head of Salhi’s boss, 54-year-old Herve Cornara, tied to the gates of the factory near two flags on which were written the Muslim profession of faith.
Prime Minister Manuel Valls told French television on Sunday that the world was engaged in a “war against terrorism”.
“We cannot lose this war because it’s fundamentally a war of civilisation. It’s our society, our civilisation that we are defending,” Valls told iTELE rolling news channel.
France is facing “a major terrorist threat” which needs to be fought “over the long term”, warned the prime minister.
It’s not a question of whether there will be another attack, but “when” and “where”, stressed Valls.
It also emerged Sunday that Salhi and Cornara may have quarrelled just two days before the killing.
According to sources close to the investigation, one of the firm’s employees said Salhi had dropped a crate of expensive materials, was reprimanded by his boss and voices were raised.
Anti-terrorist authorities have identified 473 people who have left France to fight in Iraq or Syria and Prime Minister Manuel Valls said earlier Sunday that 1,800 people in France were “linked” in some way to the jihadist cause. -AFP