Masked French police have taken the man who admitted beheading a businessman to the suspect's home to search it.
A security official said they are trying to find his passport, to determine if he travelled abroad.
French TV showed police escorting a handcuffed Yassine Salhi wearing jeans, a knee-length djellabah robe and a loose towel over his head to mask his face into his home in the town of Saint-Priest, outside the city of Lyon.
The truck deliveryman and father of three with a history of ties to Islamic extremists admitted earlier to the killing of the manager of the transport company that had employed him since March.
He allegedly crashed a truck into a US-owned chemical warehouse on Friday, setting off an explosion, and hung his employer's head on the factory's gate. He was quickly arrested afterward.
Salhi and police spent a little over an hour in his home. It was not immediately clear if police found what they were looking for. Sirens blaring, the police returned him to a Lyon police station where he was initially questioned.
He was expected to be transported to France's counter-terrorism police headquarters near Paris.
Officials say after the attack he sent a "selfie" of himself and the victim to a Canadian mobile phone number.
Investigators have found no links to any international terror group in the attack. After two days in custody for questioning in Lyon, Salhi's wife and sister were released.
French police have lifted a 48-hour secure perimeter around the site of the warehouse in Saint-Quentin-Fallavier near Lyon, allowing for the first pictures that show the damage sustained in the blast.
The severed head appeared to imitate a practice of the radical Islamic State group of beheading prisoners and displaying their heads publicly. It came days after the militants urged attacks during the Muslim holy month of Ramadan. French authorities say Salhi had links to radical Salafists in the past.
Prime Minister Manuel Valls said that "we cannot accept barbarity" and estimated 10,000 to 15,000 Salafists - who preach an ultraconservative form of Islam - were present in France.
"We are living under a major terrorist threat, and this terrorist threat is going to last," Valls said told i-Tele TV. "We should know we're going to fight this terrorism over the long term."