In the horrific attack near Lyon, which took place last Friday, Yassin Salih, 35, killed and beheaded his boss, Hervé Cornara, 54, at a parking lot near the Air Products chemicals factory on the edge of Saint-Quentin-Pallavier.
Posing as an Isis (Islamic State) executioner, he placed his victim's head at his feet, shot a selfie and sent it using WhatsApp to a friend who had actually joined Isis in Syria.
He then hung Mr Cornara's head on the factory's railings, between two Isis black flags.
Finally, he tried to drive a truck into a shed filled with gas bottles in order to cause a major explosion, but was intercepted by the fire brigade.
This barbaric crime prompted shock and horror across France.
The day afterwards, Libération, the liberal daily, ran the headline: "Jihad nauseam" - a pun on "jihad" and the Latin expression "ad nauseam". The National Council of the French Muslim Religion issued a formal condemnation.
The beheading occurred almost six months after the massacres at the satirical magazine Charlie Hebdo and at a kosher supermarket in Paris, which left 20 dead.
It also took place on the same day as a wave of Isis-related terror attacks in Tunisia and Kuwait.
On Friday, President François Hollande convened a special cabinet meeting to discuss the danger, and raised the security level in France to its highest possible point.
It seems that Yassin Salih had quarrelled with Mr Cornara on a work matter two days before killing him.
Mr Cornara, the manager of a delivery company, was said to be a warm and generous person but got angry with Salih when he dropped a fragile piece of equipment.
Other reports suggest Salih could have been in the middle of a domestic crisis, and that his wife had threatened to divorce him.
Nevertheless, French police say they believe that the evidence for a terrorist operation is overwhelming.
Salih, a French Muslim of north African descent, has been involved with jihadist cells since 2006. The friend to whom he forwarded the beheading selfie - named as Sébastien-Younes V - is a French-Algerian extremist who left for Syria in November, along with his wife and 18-month-old child.
Both men seem to have been influenced by Frederic Jean Salvi - also known as "Ali" or the "Great Ali" - a drug dealer who converted to Islam while in jail and subsequently organised an underground Salafist mosque in Pontarlier, eastern France - Salih's place of birth.
