The suspected militant Islamist accused of decapitating his boss and attempting to blow up a gas plant in southeastern France had taken a macabre "selfie" with the severed head before his arrest, a source close to the investigation said on Saturday.
Yassim Salhi, a 35-year-old of North African parentage, is being held in the city of Lyon after ramming his delivery van into a warehouse storing gas containers on Friday. He was apprehended minutes later while opening canisters containing flammable chemicals.
Police found the head of Herve Cornara, manager of the transport firm that employed Salhi, attached to a fence at the plant owned by US group Air Products, framed by black and white flags bearing Islamic slogans.
President Francois Hollande, dealing with new security fears six months after Islamist gunmen killed 17 people at the offices of satirical weekly Charlie Hebdo and a Jewish foodstore, said the incident clearly amounted to a terrorist attack.
Salhi, whose wife and sister are also being detained along with a fourth person, is known to have associated with Islamists over more than a decade and had previously been flagged as a potential risk. But there has so far been no claim of responsibility for the attack.
Paris public prosecutor Francois Molins said on Friday that investigators would take time to piece together the sequence of events at the plant in Saint Quentin-Fallavier, 30 km (20 miles) south of Lyon, and establish whether Salhi was acting alone.
Examination of the suspect's mobile phone revealed that he had sent his macabre self-portrait via the Whatsapp messaging application to a user account associated with a North American number, a law enforcement source said on Saturday. The ownership of the account was not yet clear.
The body of Cornara, 54, also bore signs of strangulation suggesting that he may have been killed at an unknown location prior to his decapitation.
Investigators searching his home in Saint-Priest, near Lyon, seized a laptop, a tablet computer and a fake pistol but found no trace of explosives or radical propaganda.
"We don't know whether we're dealing with a fundamentalist who just lost it or a real terrorist," the source said.
THREE ATTACKS ON SAME DAY
The latest attack in France occurred on the same day that a gunman killed 39 people at a Tunisian beachside hotel and an Islamic State suicide bomber killed two dozen and wounded more than 200 at a mosque in Kuwait.
French authorities said there was no connection between the attacks and nothing to indicate that the industrial site had been targeted because of its US ownership.
"There is no other link other than to say that terrorism is our common enemy," said Hollande said after rushing back to Paris from an EU summit in Brussels.
Unlike two of the gunmen behind the January attacks, Salhi does not have a criminal record. But the fact he was flagged as a risk between 2006 and 2008 and known to have since maintained radical Islamist links is raising new questions about the security services and their effectiveness.
Opposition leader and former President Nicolas Sarkozy, who was in office when Salhi's surveillance was lifted in 2008, said on Friday his conservative Les Republicains party had been urging the government "for several weeks" to tighten security.
The attack may also renew tensions surrounding France's 5 million Muslims, despite the widespread revulsion expressed by many Islamic leaders and communities over the Charlie Hebdo killings.
While Salhi's Islamist connections were known to authorities, neighbours at his family home in Saint-Priest, a quiet suburb, expressed disbelief.
"They are a very normal family," said a 46-year-old housewife who gave her name as Brigitte. "I only talked with madame; he didn't say hello or goodbye."