The Champs Elysee attacker, like the majority of France’s terrorists, was believed to be “known to police”.
The man has not been officially identified.
But, if it is confirmed that he was familiar to authorities, it will raise yet more questions about how able Europe’s police forces are to cope with the large number of potential attackers.
It takes at least 20 police to follow one person around the clock: the simple fact is that police have to chose who to follow. And sometimes they make the wrong decision.
All three of the terrorists in the January 2015 Charlie Hebdo attacks – Cherif and Said Kouachi, and Amedy Coulibaly – were known to police.
The Kouachi brothers first came to attention playing sport in the Buttes-Chaumont park in Paris, where they befriended more than a dozen other similar young men, who would all eventually be known to police for a terrorism plot to fight as jihadis in Iraq.
With their friends from the park, they fell under the spell of a radical preacher named Farid Benyettou, who mentored many of the young and disenfranchised youths at the local mosque.
Said Kouachi attended the sessions, although he was less involved than his younger brother.
Cherif Kouachi was jailed for his involvement in that plot – telling police of his plans to travel to Syria and fight for jihadist groups. And, while in prison, he became yet more radicalized – this time by Djamel Beghal, also of Algerian origin, who was jailed for plotting to attack the US Embassy in Paris in 2001.
Coulibaly met Cherif Kouachi in prison, while serving time for armed robbery – the men grew close, thanks to their shared appreciation of Beghal’s radical teachings.
After their release from prison, the trio plotted to break another Algerian out of prison.
Coulibaly was arrested in May 2010 with a huge cache of arms, and sent to prison – there was not enough evidence to prosecute Cherif Kouachi, however – despite police finding plans for a terror attack on his computer.
In 2011 Cherif Kouachi is believed to have travelled to Yemen.
The brothers and Coulibaly were placed under police surveillance for three years – eventually dropped in the summer of 2014.
And several of the 11 men thought to be behind the November 2015 Paris attacks were well known to police, and had travelled to Syria.
The attacks are suspected to have been masterminded by Abdelhamid Abaaoud, a Belgian national killed in a police raid in Saint-Denis, northern Paris, a few days later.
Abaaoud was a known extremist who had previously been implicated in several jihadi attacks and plots in France.
He appears to have left Belgium in late 2013 or early 2014, passing through Cologne-Bonn airport on his way to Syria, where he rose to head an Isis unit planning attacks in Europe. He was initially believed to have been in Syria at the time of the attacks, until French intelligence officials learnt that he was back in France.
Another of the 11, Foued Mohamed Aggad, 23, was said to have travelled to Syria too - as a member of a group, including his brother, who had gone to fight there in 2013.
Samy Amimour, 28, was detained in October 2012 on suspicion of “associating with terrorists” and planning to leave for Yemen, and was held for four days. Released, he went to Syria in September 2013, violating his parole.
Bilal Hadfi, 20, left for Syria five weeks after the Charlie Hebdo attacks: police raided his house in March 2015, but to no avail. Only two of the 11 known gang members survived: Salah Abdeslam, arrested on March 18, 2016 after four months on the run, and Mohamed Abrini, arrested in Brussels on April 8.
The 2016 Nice attack, in which 86 people were killed when a cargo truck was driven into crowds of people celebrating Bastille Day, was also carried out by an Islamist extremist known to police.
Mohamed Lahouaiej Bouhlel received a six-month suspended prison sentence for attacking a person involved in a road accident with a piece of wood and he was facing allegations of domestic abuse, theft and "use of weapons".