Jean-Pierre Filiu, professor of Middle Eastern Studies at Sciences Po, Paris School of International Affairs, said that many recruits were “born again” when they enter Islamic State (IS).
He told the Irish Examiner this was not a slow process of radicalisation, but a “brutal shock”.
This comes as French prime minister Manuel Valls said that Tunisian Mohamed Lahouaiej Bouhel was “radicalised very quickly”.
Friends and relatives said the 31-year old was not religious and, at least until recently, drank alcohol, smoke marijuana, and ate pork.
IS claimed the attack on Saturday and asserted that Bouhel, a father of three, was “one of the soldiers of Islamic State”.
“The Nice killer is only one among many with a record of petty crime and a negligible level of [religious] observance,” said Prof Filiu, author of From Deep State to Islamic State.
“While entering ISIS, the recruits are literally ‘born again’, with the symbolic change of their names.
“This is a brutal shock and not a slow process of ‘radicalisation’, a word that I find misleading since it nurtures the illusion that such process could be detected, stopped and eventually reversed.”
He said France is host to the largest Muslim community in Europe.
“This is a reality that ISIS cannot accept and will fight to the end, as the targeting of its terror attacks in France has proven,” he said.
“But the jihadi plan to stir sectarian violence in France has so far failed, even though tensions run high and a populist discourse is more and more vocal.”
He said the “immense majority” of terrorist tip-offs come from the Muslim community and that, in Nice, imams “preaching against ISIS have been threatened by jihadi sympathisers”.
Meanwhile, Public Expenditure Minister Paschal Donohoe defended the use of Shannon Airport by US troops after TD Clare Daly said it made Ireland “a terrorism target”.