When suburban deliveryman Yassin Sahli set off for work on Friday, his wife said it seemed just like any other day.

Within hours, the 35-year-old father of three was arrested on suspicion of beheading his boss, then ramming their van into an industrial gases site in southeast France, setting off an explosion that authorities called an attempted act of terrorism.

"Yesterday he was at work, he came home as usual. We spent a normal evening and in the morning he left for work and didn't come home between noon and 2. I was waiting for him," a woman identified as his wife told Europe 1 radio.

Sources close to the investigation said the wife, who has not been officially named, was subsequently arrested and was being held by police for questioning.

Yassin Sahli was named as the chief suspect by Interior Minister Bernard Cazeneuve in a brief statement at the site of the attack in the town of Saint-Quentin Fallavier, 30 km (20 miles) south of Lyon.

Very little has been officially released on his background.

Yet according to his wife's brief radio interview, theirs was an ordinary Muslim family living in the Lyon suburb of Saint-Priest, an account shared by neighbours who said contact with Sahli was limited to simple greetings.

He and his wife lived with their three children, aged between six and nine, on the ground floor of a three-storey, nondescript social housing block.

The area is quiet, with green spaces, clean streets and a new tram link to the centre of Lyon. It is far from the stereotypical image of a run-down city suburb.

"They are a very normal family," a neighbour who gave her name as Brigitte said. I only talked with madame, he didn't say hello or goodbye," the 46-year-old housewife said.

Though Sahli, of North African origin, had no criminal record, Cazeneuve said he was categorised by security services as far back as 2006 as someone at risk of being radicalised.

While that status allowed security forces to discreetly keep tabs on him, they did not see fit to renew it in 2008, although he was known to have contact with radical Islamists in France.

However, he was back on the radar of the DGSI domestic security service for at least the past two years and was described in 2013 as a "hardcore Muslim" in one intelligence memo, according to RTL radio.

Another memo dating from May 2014 said he had undergone a "radical" change, losing weight and shaving his beard. It said he was often away from home for unexplained absences of several weeks at a time.

The note said he held meetings at his home, hosting men who wore combat fatigues. Doorstep chatter with them was peppered with references to jihad, said RTL, citing the memo.

Sahli had been living in Saint-Priest for around six months. Before that, the Est Republicain newspaper said the suspect, whose late father was Algerian and mother Moroccan, lived in Pontarlier near the Swiss border. The town is home to a mosque known for the virulent views of its preacher, who has since left France.