France Terror Attack: Decapitated Head of Suspect's Boss Found on Factory Fence

— -- The man who is believed to have decapitated his boss and caused an explosion at an American-owned energy factory in France was let onto the property today because he regularly made deliveries there, investigators say.

French prosecutor Francois Molins said the suspect was discovered while he was opening bottles of chemicals after ramming a car into canisters of gas.

Molins said the utility car from the transport company for which he worked entered the factory's property at 9:28 a.m. local time.

Factory employees knew the driver and let him in the gate.

A nearby camera recorded the vehicle accelerating toward a covered hangar at 9:35 a.m. and an explosion was heard a minute later.

Firefighters who were practicing nearby arrived at the scene quickly but did not find the suspect until about 10 a.m. when he was in a second hangar where there were gas canisters, acetone and liquid air, Molins said.

The decapitated body was found in the front seat of the truck along with a knife that is now being analyzed. The head of the victim was found pitched on a fence surrounding the factory with two flags with a Muslim profession of faith written across them.

The investigation into the attack is ongoing and among the primary questions for police are when and where the body was decapitated, including whether it was after death.

The suspect did not identify himself to the firefighters but the employees were able to identify him, Molins said.

He has since been identified as Yassine Salhi and was taken into custody, French Minister of Interior Bernard Cazeneuve said earlier today. The suspect has no criminal record but was the subject of a “Fiche S” designation – for “security of the state” – in 2006 because of suspected radicalization, Cazeneuve said. That status was not renewed in 2008.

Cazeneuve said Salhi is originally from Saint-Priest, Lyon, which is about 12 miles away from Saint-Quentin-Fallavier, the site of the factory.

The victim’s name has not been released but Molins said he was the 54-year-old owner of the transportation company where Salhi has worked since March.

In addition to Salhi, three others have been arrested in connection to the case: his wife of 10 years, his sister and another associate. Their names have not been publicly released.

French President Francois Hollande said here were inscriptions on the body.

"It is a terrorist attack, there is no doubt about that,” Hollande said from Brussels, where he is attending an EU summit.

The attack took place on the grounds of a factory owned by Pennsylvania-based Air Products & Chemicals, which produces industrial gases and says it’s the world’s leading supplier of helium.

"We can confirm that an incident occurred at our facility in L'Isle-d'Abeau, France this morning. Our priority at this stage is to take care of our employees, who have been evacuated from the site and all accounted for,” the company said. “Emergency services are on site and have contained the situation. The site is secure. Our crisis and emergency response teams have been activated and are working closely with all relevant authorities. Further information will be released as soon as it becomes available."

At least 17 people have been killed in terror-related violence in France this year. In January, gunmen attacked the satirical newspaper Charlie Hebdo. The men suspected in that attack were later killed in raids at a Kosher supermarket and print shop.

Last September, in a 42-minute video address, ISIS spokesman Abu Muhammad al-Adnani urged Muslims around the globe to target, specifically, the "spiteful and filthy" French.

A senior U.S. intelligence official told ABC News that the timing of today's attack is not necessarily tied to the Muslim religious period of Ramadan.

"It is fair to say that there has been a heightened awareness in general for the homeland, but have not seen it tied to Ramadan," the official said. "Overseas, ISIL has referenced Ramadan, however."

White House press secretary Josh Earnest released a statement today about the three attacks.

"The United States condemns in the strongest terms the terrorist attacks in France, Kuwait, and Tunisia today. Our thoughts and prayers are with the victims of these heinous attacks, their loved ones, and the people of all three countries," the statement read.

"As the President has discussed with his French, Kuwaiti, and Tunisian counterparts in recent weeks, we are resolute and united in our shared effort to fight the scourge of terrorism.”

ABC News' Joseph Simonetti and The Associated Press contributed to this report.

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